media: venus: support frame rate control

Add encoder control for enabling/disabling frame rate control via
V4L2_CID_MPEG_VIDEO_FRAME_RC_ENABLE. It is enabled by default.

Signed-off-by: Jeffrey Kardatzke <jkardatzke@google.com>
Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>