media: vicodec: rename v4l2_fwht_default_fmt to v4l2_fwht_find_nth_fmt

Rename 'v4l2_fwht_default_fmt' to 'v4l2_fwht_find_nth_fmt'
and add a function 'v4l2_fwht_validate_fmt' to check if
a format info matches the parameters.
This function will also be used to validate the stateless
params when adding support for stateless codecs.

Signed-off-by: Dafna Hirschfeld <dafna3@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>