drm/amdgpu: fix incorrect number of active RBs for gfx11

The RB bitmap should be global active RB bitmap &
active RB bitmap based on active SA.

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