[media] s5p-fimc: Correct color format enumeration

Replace fimc_find_format() and find_mbus_format() with single function
that can return a pointer to the private format description based
on fourcc, media bus code or index in the table.

Create separate VIDIOC_ENUM_FMT ioctl handlers for video capture
and mem-to-mem video node. This is needed because some formats are
valid only for the video capture and some only for the mem-to-mem
video node.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>