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

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 <[email protected]>
Acked-by: Jasdeep Dhillon <[email protected]>
Tested-by: Daniel Wheeler <[email protected]>
Signed-off-by: Cruise Hung <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>