UPSTREAM: v4l: add V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME.

UPSTREAM: v4l: add V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME.

Some drivers also need a control like
V4L2_CID_MPEG_MFC51_VIDEO_FORCE_FRAME_TYPE to force an encoder
key frame. Add a general V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME
so the new drivers and applications can use it.

Signed-off-by: Wu-Cheng Li <wuchengli@chromium.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
(cherry picked from commit 0c8485ca3f2aaf7842d45ba24c667a9492c9900f)
Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
BUG=chromium:572825
TEST=Build and boot oak-rev5 to UI
TEST=emerge-smaug chromeos-kernel-3_18

Reviewed-on: https://chromium-review.googlesource.com/328870
Commit-Ready: Daniel Kurtz <djkurtz@chromium.org>
Tested-by: Daniel Kurtz <djkurtz@chromium.org>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Change-Id: I45de3048d41edbe443b3d202c17e79f2d448213b
Signed-off-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Yakir Yang <ykk@rock-chips.com>