Revert "drm/amdgpu/gfx10: enlarge CP_MEC_DOORBELL_RANGE_UPPER to cover full doorbell."

This reverts commit 1c0b0efd.

Reason for revert: Side effect of enlarging CP_MEC_DOORBELL_RANGE may
cause some APUs fail to enter gfxoff in certain user cases.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org