pmbootstrap init: kernel selection / remove linux-pmos-lts (#1363)

* As discussed in IRC/matrix, we're removing `linux-postmarketos-lts`
  for now. The kernel isn't used right now, and we save lots of
  maintenance effort with not updating it every week or so.
* new config option `"kernel"` with possible values:
  `"downstream", "mainline", "stable"` (downstream is always
  `linux-$devicename`)
* ask for the kernel during `pmbootstrap init` if the device package
  has kernel subpackages and install it in `_install.py`
* postmarketos-mkinitfs: display note instead of exit with error when
  the `deviceinfo_dtb` file is missing (because we expect it to be
  missing for downstream kernels)
* device-sony-amami:
  * add kernel subpackages for downstream, mainline
  * set `deviceinfo_dtb`
* device-qemu-amd64: add kernel subpackages for stable, lts, mainline
* test cases and test data for new functions
* test case that checks all aports for right usage of the feature:
  * don't mix specifying kernels in depends *and* subpackages
  * 1 kernel in depends is maximum
  * kernel subpackages must have a valid name
  * Test if devices packages reference at least one kernel
* Remove `_build_device_depends_note()` which informs the user that
  `--ignore-depends` can be used with device packages to avoid building
  the kernel. The idea was to make the transition easier after a change
  we did months ago, and now the kernel doesn't always get built before
  building the device package so it's not relevant anymore.
* pmb/chroot/other.py:
  * Add autoinstall=True to kernel_flavors_installed(). When the flag
    is set, the function makes sure that at least one kernel for the
    device is installed.
  * Remove kernel_flavor_autodetect() function, wherever it was used,
    it has been replaced with kernel_flavors_installed()[0].
* pmb.helpers.frontend.py: remove code to install at least one kernel,
  kernel_flavors_installed() takes care of that now.

pmb/helpers/frontend.py

@@ -44,41 +44,16 @@ import pmb.parse
 import pmb.qemu
 
 
-def _build_device_depends_note(args, pkgname):
-    """
-    Previously 'pmbootstrap build device-...' built the device package in the
-    native chroot without installing its dependencies (e.g. armhf kernel!) and
-    created a symlink to all supported architectures.
-
-    Not installing depends while building is incompatible with how Alpine's
-    abuild does it, so we changed the behavior. Now pmbootstrap reads the
-    device's architecture from the deviceinfo file and automatically builds
-    for that architecture, if you did not specify any architecture. And the
-    dependencies get installed correctly before the build.
-
-    To make migration easier for the users, we show a hint if building a device
-    package was requested.
-    """
-    # Only relevant for device packages when -i is not set
-    if not pkgname.startswith("device-") or getattr(args, "ignore_depends"):
-        return
-
-    device = pkgname.split("-", 1)[1]
-    logging.info("NOTE: " + device + "'s kernel will be installed as dependency"
-                 " before building (old behavior: 'pmbootstrap build -i')")
-
-
 def _parse_flavor(args):
     """
     Verify the flavor argument if specified, or return a default value.
     """
-    # Make sure, that at least one kernel is installed
+    # Install at least one kernel and get installed flavors
     suffix = "rootfs_" + args.device
-    pmb.chroot.apk.install(args, ["device-" + args.device], suffix)
+    flavors = pmb.chroot.other.kernel_flavors_installed(args, suffix)
 
     # Parse and verify the flavor argument
     flavor = args.flavor
-    flavors = pmb.chroot.other.kernel_flavors_installed(args, suffix)
     if flavor:
         if flavor not in flavors:
             raise RuntimeError("No kernel installed with flavor " + flavor + "!" +
@@ -116,11 +91,6 @@ def build(args):
     if args.strict:
         pmb.chroot.zap(args, False)
 
-    # Detect old usage for device- packages
-    if not args.ignore_depends:
-        for package in args.packages:
-            _build_device_depends_note(args, package)
-
     # Set src and force
     src = os.path.realpath(os.path.expanduser(args.src[0])) if args.src else None
     force = True if src else args.force