drm/amdgpu/gfx9: fix the doorbell missing when in CGPG issue.

If GC has entered CGPG, ringing doorbell > first page doesn't wakeup GC.
Enlarge CP_MEC_DOORBELL_RANGE_UPPER to workaround this issue.

Signed-off-by: Yifan Zhang <yifan1.zhang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>