media: imx: allow to build with COMPILE_TEST

Allow building this driver for other platforms under COMPILE_TEST.

Suggested-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Steve Longerbeam <steve_longerbeam@mentor.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>