drm/amd/display: Warn instead of error on REG_WAIT timeout

[Why]
DC warns when a REG_WAIT takes a while and full-on errors
with stack dump on REG_WAIT timeout.  Most of the time it isn't
a real issue.

[How]
Make DC cool its jets - taking a while is a debug message (because
it is not something that normal users should need to be aware of),
and timeouts are warnings (because it technically shouldn't
happen, but it's not a big deal if it does)

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>