pmb/install: Add option to create single combined boot/root partition

With recent rework in postmarketos-initramfs, we no longer need to mount
the /boot partition in the initramfs (assuming initramfs-extra is not
used). On devices that boot without accessing the boot file system (e.g.
Android boot images, fastboot, ...), that makes it possible to install
postmarketOS on a single (potentially encrypted) partition that contains
both root (/) and /boot files.

This avoids the extra complexity of the subpartition setup we usually use
on such devices, and also avoids having to flash two partitions (when using
--split to avoid the subpartitions).

Add a --single-partition option to pmbootstrap install that allows
installing postmarketOS in this mode. For now this is just an option that
must be selected explicitly, in the future we could choose to make this the
default for Android-based devices with a large enough boot partition.

Part-of: https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/-/merge_requests/2512

pmb/parse/arguments.py

@@ -120,6 +120,14 @@ def arguments_install(subparser: argparse._SubParsersAction) -> None:
         choices=[512, 2048, 4096],
     )
 
+    ret.add_argument(
+        "--single-partition",
+        action="store_true",
+        help="Create a single partition that contains both boot and root files."
+        " This can be used on devices that boot without mounting the boot file"
+        " system (e.g. Android boot images or fastboot).",
+    )
+
     # Image type
     group_desc = ret.add_argument_group(
         "optional image type",

pmb/parse/deviceinfo.py

@@ -118,6 +118,7 @@ class Deviceinfo:
     # bootloader
     flash_method: str = ""
     boot_filesystem: str | None = ""
+    create_initfs_extra: bool | None = False
 
     # flash
     flash_heimdall_partition_kernel: str | None = ""