drm/amdgpu: revise RLCG access path

what changed:
1)provide new implementation interface for the rlcg access path
2)put SQ_CMD/SQ_IND_INDEX to GFX9 RLCG path to let debugfs's reg_op
function can access reg that need RLCG path help

now even debugfs's reg_op can used to dump wave.

tested-by: Monk Liu <monk.liu@amd.com>
tested-by: Zhou pengju <pengju.zhou@amd.com>
Signed-off-by: Zhou pengju <pengju.zhou@amd.com>
Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Emily Deng <Emily.Deng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>