media: Request API is no longer experimental

The Request API is currently used and specified as part of the
Memory-to-memory Stateless Video Decoder Interface [1].

This can now be considered as non-experimental and stable, given
the decoder API has been used by products since a couple years,
supported by several drivers and userspace frameworks,

[1] Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>