media: imx: enable V4L2_PIX_FMT_XBGR32, _BGRX32, and _RGBX32

Now that proper V4L2 pixel formats exist for all 32-bit RGB
permutations, drop support for the poorly defined legacy format
V4L2_PIX_FMT_BGR32.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>