This commit implements frame decimation for stk1160, which allows
to support format changes instead of a static frame size.
The stk1160 supports independent row and column decimation, in two
different modes:
* set a number of rows/columns units to skip for each unit sent.
* set a number of rows/columns units to send for each unit skipped.
This effectively allows to achieve different frame scaling ratios.
The unit number can be set to either two row/columns sent/skipped,
or four row/columns sent/skipped. Since the video format (UYVY)
has 4-bytes, using a unit number of two row/columns results
in frame color 'shifting', so set to four row/columns sent/skipped.