drm/radeon: disable tests/benchmarks if accel is disabled

The tests are only usable if the acceleration engines have
been successfully initialized.

Based on an initial patch from: Alex Ivanov <gnidorah@p0n4ik.tk>

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

diff --cc drivers/gpu/drm/radeon/radeon_device.c
Simple merge