drm/radeon: tweak ACCEL_WORKING2 query for hawaii

Return 2 so we can be sure the kernel has the necessary
changes for acceleration to work.

Note: This patch depends on these two commits:
 - drm/radeon: fix cut and paste issue for hawaii.
 - drm/radeon: use packet2 for nop on hawaii with old firmware

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Andreas Boll <andreas.boll.dev@gmail.com>
Cc: stable@vger.kernel.org