v4l2-ctrl: Make display delay and display enable std controls

Make display delay and display delay enable MFC controls standard v4l
controls. This will allow reuse of the controls for other decoder
drivers. Also the new proposed controls are now codec agnostic because
they could be used for any codec.

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