FROMGIT: media: v4l2-ctrl: Add frame-skip std encoder control

Adds encoders standard v4l2 control for frame-skip. The control
is a copy of a custom encoder control so that other v4l2 encoder
drivers can use it.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Bug: 151414336
Change-Id: Ie6b116d9a3c4954bb21f26e82a5a27370cfa1c8d
(cherry picked from commit 1edcd843ef8b198d391ade1828c0c84acc3b9c4c
 https://git.linuxtv.org/svarbanov/media_tree.git

 venus-for-next-v5.10)
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>