[media] media: ti-vpe: vpe: Add RGB565 and RGB5551 support

VPE hardware can generate output in RGB565 or in RGB5551 format.
Add these formats in the supported format list for CAPTURE stream.
Also, for RGB5551 format, the alpha component is not processed,
so the alpha value is taken from the default color.
Set the default color to make alpha component full when the dst
format is of RGB color space.

Signed-off-by: Nikhil Devshatwar <nikhil.nd@ti.com>
Signed-off-by: Benoit Parrot <bparrot@ti.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>