[media] dt3155v4l: drop CONFIG_DT3155_STREAMING

No need to do this as a config option. Just support both MMAP and read()
methods like any other driver.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>