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.