media: imx: utils: Split find|enum_format into fourcc and mbus functions

To make the code easier to follow, split up find_format() into separate
search functions for pixel formats and media-bus codes, and inline
find_format() into the exported functions imx_media_find_format()
and imx_media_find_mbus_format().

Do the equivalent for enum_format().

Also add comment blocks for the exported find|enum functions.

The convenience functions imx_media_find_ipu_format() and
imx_media_enum_ipu_format() can now be made inline and moved to
imx-media.h.

Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>