media: rkvdec: Move H264 SPS validation in rkvdec-h264

No functional change, this moves H264 specific validation into the H264
specific code. This is in preparation of improving this validation and
reusing it when VIDIOC_STREAMON is called.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>