drm/amd/display: Added HPO HW control shutdown support

drm/amd/display: Added HPO HW control shutdown support

[Why]
HPO is only used for DP2.0. HPO HW control should be
disable when not being used to save power.

[How]
Shutdown HPO HW control during init hw.
Shutdown HPO HW control during stream disable.
Enable HPO HW control during stream enable if DP2.0.

Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Jake Wang <haonan.wang2@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>