drm/amdgpu/sdma4: Enable sdma poll mem addr on vega10 for SRIOV

While doing flr on VFs, there is possibility to lost the doorbell
writing for sdma, so enable poll mem for sdma, then sdma fw would
check the pollmem holding wptr.

Signed-off-by: Frank Min <Frank.Min@amd.com>
Signed-off-by: Xiangliang.Yu <Xiangliang.Yu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>