media: allegro: add control to disable encoder buffer

The encoder buffer can have a negative impact on the quality of the
encoded video.

Add a control to allow user space to disable the encoder buffer per
channel if the VCU supports the encoder buffer but the quality is not
sufficient.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>