media: stm32-dcmi: add support of BT656 bus

Add support of BT656 embedded synchronization bus.
This mode allows to save hardware synchro lines hsync & vsync by replacing
them with synchro codes embedded in data stream.
This bus type is only compatible with 8 bits width data bus.
Due to reserved values 0x00 & 0xff used for synchro codes, valid data vary
from 0x1 to 0xfe, this is up to sensor to clip accordingly pixel data. As
a consequence of this clipping, JPEG is not supported with this bus type.
DCMI crop feature is also not available with this bus type.

Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>