drm/amd/display: Turn on phantom OTG before disabling phantom pipe

[Description]
- Proper phantom pipe disable sequence was missing in
  commit_planes_for_stream
- If disabling phantom pipe, turn on phantom OTG first, and turn
  off the phantom OTG after the plane is disabled
- Also update sequence for enabling / disabling phantom streams
  (apply_ctx_to_hw). When enabling phantom pipes, enable before
  doing front end programming for phantom pipes. If disabling
  phantom pipes, disable after front end programming (i.e. after
  phantom plane disable)
- TODO: Still need to properly handle transition case when a phantom
  pipe is transitioned directly into a real pipe (need to fully disable
  the phantom pipe first)

Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>