The ov7670 has the test pattern generator features.  This makes use of
it through V4L2_CID_TEST_PATTERN control.

Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: NSakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>