linux-imx

drm/nouveau: fix build failures on all non ARM.

gk20a is an ARM only GPU, so we can just do the correct thing on
ARM but fail on other architectures. The other option was to use
SWIOTLB as the define, which means phys_to_page exists, but
this seems clearer.

Signed-off-by: Dave Airlie <airlied@redhat.com>