drm/amd/display: solve regression in update phy state refactor

[Why]
There is a coding error when moving dp disable link phy to
hw sequencer, where the receiver power control is missed during
this refactor.

[how]
1. Add back missing receiver power control in disable link phy.
2. minor modifications to ensure there is no undesired sequence
changes in dp link enable/disable.

Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Reviewed-by: Martin Leung <Martin.Leung@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>