[media] smiapp: Implement the test pattern control

Add support for the V4L2_CID_TEST_PATTERN control. When the solid colour
mode is selected, additional controls become available for setting the
solid four solid colour components.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>