drm/amdgpu: switch to amdgpu_sriov_rreg/wreg

Instead of ip specific implementation for rlcg
indirect register access

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Zhou, Peng Ju <PengJu.Zhou@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>