media: uapi: Move parsed VP8 pixel format out of staging

Since we are ready to stabilize the VP8 stateless API,
move the parsed VP8 pixel format.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>