[media] vimc: sen: Integrate the tpg on the sensor

Initialize the test pattern generator on the sensor
Generate a colored bar image instead of a grey one

Signed-off-by: Helen Koike <helen.koike@collabora.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>