media: i2c: adv7180: Add support for the test patterns

ADV7180 has a built-in mechanism to generate some video patterns,
which is very useful for debug/bring-up activities.

Add support for it.

The test_pattern parameter can be one of the following values:

	0:	"Single color"
	1:	"Color bars"
	2:	"Luma ramp"
	3:	"Boundary box"
	4:	"Disable"

Tested on a imx6q board with an ADV7280.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>