media: uapi: move VP8 stateless controls out of staging

Until now, the VP8 V4L2 API was not exported as a public API,
and only defined in a private media header (media/vp8-ctrls.h).

The reason for this was a concern about the API not complete
and ready to support VP8 decoding hardware accelerators.

After reviewing the VP8 specification in detail, and now
that the API is able to support Cedrus and Hantro G1,
we can consider this ready.

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>