media: omap2: allow building it with COMPILE_TEST && DRM_OMAP

Now that FB_OMAP has stubs, the omap2 media drivers can be
built on ARM with COMPILE_TEST && DRM_OMAP.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>