media: uapi: move HEVC stateless controls out of staging

HEVC uAPI is used by 2 mainline drivers (Hantro, Cedrus)
and at least 2 out-of-tree drivers (rkvdec, RPi).
The uAPI has been reviewed so it is time to make it 'public' by
un-staging it.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Acked-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Tested-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>