video: fbdev: via: allow COMPILE_TEST build

This patch allows viafb driver to be build on !X86 archs
using COMPILE_TEST config option.

Since via-camera driver (VIDEO_VIA_CAMERA) depends on viafb
it also needs a little fixup.

Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>