libcamera: framebuffer: Move remaining private data to Private class

Private members of the FrameBuffer class are split between FrameBuffer
and FrameBuffer::Private. There was no real justification for this
split, and keeping some members private in the FrameBuffer class causes
multiple issues:

- Future modifications of the FrameBuffer class without breaking the ABI
  may be more difficult.
- Mutable access to members that should not be modified by applications
  require a friend statement, or going through the Private class.

Move all remaining private members to the Private class to address the
first issue, and add a Private::metadata() function to address the
second problem.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>
Tested-by: Naushir Patuck <naush@raspberrypi.com>

src/android/mm/generic_frame_buffer_allocator.cpp

@@ -32,8 +32,10 @@ class GenericFrameBufferData : public FrameBuffer::Private
 
 public:
 	GenericFrameBufferData(struct alloc_device_t *allocDevice,
-			       buffer_handle_t handle)
-		: allocDevice_(allocDevice), handle_(handle)
+			       buffer_handle_t handle,
+			       const std::vector<FrameBuffer::Plane> &planes)
+		: FrameBuffer::Private(planes), allocDevice_(allocDevice),
+		  handle_(handle)
 	{
 		ASSERT(allocDevice_);
 		ASSERT(handle_);
@@ -136,8 +138,7 @@ PlatformFrameBufferAllocator::Private::allocate(int halPixelFormat,
 	}
 
 	return std::make_unique<FrameBuffer>(
-		std::make_unique<GenericFrameBufferData>(allocDevice_, handle),
-		planes);
+		std::make_unique<GenericFrameBufferData>(allocDevice_, handle, planes));
 }
 
 PUBLIC_FRAME_BUFFER_ALLOCATOR_IMPLEMENTATION