drm/amdgpu: set CP_HQD_PQ_DOORBELL_CONTROL.DOORBELL_MODE to 1 for sriov multiple vf.

In sriov multiple vf, Set CP_HQD_PQ_DOORBELL_CONTROL.DOORBELL_MODE to 1 to read WPTR from MQD.

Signed-off-by: Emily Deng <Emily.Deng@amd.com>
Acked-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>