drm/amdgpu/virt: use kiq to access registers (v2)

For virtualization, it is must for driver to use KIQ to access
registers when it is out of GPU full access mode.

v2: agd: rebase

Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Monk Liu <Monk.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>