media: i2c: imx334: add support for test pattern generator

Add support for the imx334's test pattern generator.
By default the test pattern generator is disabled, so add support for
enabling and disabling horizontal and vertical colour bars.

Signed-off-by: Shravan Chippa <shravan.chippa@microchip.com>
Acked-by: Daniele Alessandrelli <daniele.alessandrelli@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>