media: vimc: propagate pixel format in the stream

Media bus codes were being mapped to pixelformats, which causes a
limitation on vimc because not all pixelformats can be mapped to media
bus codes.
Also, media bus codes are an internal configuration from the device.
Userspace only assures media bus codes matches between pads and expects
the image in a given pixelformat. So we can allow almost any media bus
format to be configured between pads, except for debayer that expects a
media bus code of type bayer in the sink pad.

[hverkuil-cisco@xs4all.nl: drop use of v4l2_get_fourcc_name: not yet available]
[hverkuil-cisco@xs4all.nl: made vimc_mbus_list static]

Signed-off-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>