drm/amd/display: Fix DMUB outbox trace in S4 (#4465)

[Why]
DMUB Outbox0 read/write pointer not sync after resumed from S4.
And that caused old traces were sent to outbox.

[How]
Disable DMUB Outbox0 interrupt
and clear DMUB Outbox0 read/write pointer when resumes from S4.
And then enable Outbox0 interrupt before starts DMCUB.

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Jasdeep Dhillon <jdhillon@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Cruise Hung <Cruise.Hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>