drm/amdgpu: add support for SDMA on multiple AIDs

Initialize SDMA instances on each AID.

v2: revise coding fault in hw_fini

Signed-off-by: Le Ma <le.ma@amd.com>
Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>