drm/amd/display: generic indirect register access

add generic indirect register access following our register access pattern

this will make it easier to review code and programming sequence,
with all the complexity hidden in macro

Signed-off-by: Tony Cheng <tony.cheng@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>