drm/radeon: fix build on 64-bit with some compilers.

drivers/gpu/drm/radeon/radeon_test.c:45: undefined reference to `__udivdi3'

Reported-by: Mr. James W. Laferriere <babydr@baby-dragons.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>