drm/amdgpu/gfx8: drop per-APU CU limits

Always use the max for the family rather than the per sku limits.
This makes sure the mask is always the max size to avoid reporting
the wrong number of CUs.

Reviewed-by: Alex Xie <AlexBin.Xie@amd.com>
Reviewed-by: Andres Rodriguez <andresx7@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>