drm/amd/display: program PSR2 DPCD Configuration

[Why]
To support PSR2 Source DPCD configuration

[How]
Update the PSR2 Source DPCD settings while the PSR2 enabled

Signed-off-by: David Zhang <dingchen.zhang@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>