drm/amdgpu: add indirect r/w interface for smn address greater than 32bits

On multiple AIDs platform, bit[34:32] in SMD address is leveraged to access
nonAID0 register smn address and new PCI_INDEX_HI register is introduced
to access the higher bits.

v2: rebase on latest register accessors (Alex)

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>