drm/amdgpu: Use GPU VA space for IH v4.4.2 in APU

For IH ring buffer and read/write pointers, use GPU VA space rather than
Guest PA on APU configs. Access through Guest PA doesn't work when IOMMU
is enabled. It is also beneficial in NUMA configs as it allocates from
the closest numa pool in a numa enabled system.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Harish Kasiviswanathan <Harish.Kasiviswanathan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>