drm/amd/display: Check zero planes for OTG disable W/A on clock change

drm/amd/display: Check zero planes for OTG disable W/A on clock change

[Why]
A display clock change hang can occur when switching between DIO and HPO
enabled modes during the optimize_bandwidth in dc_commit_state_no_check
call.

This happens when going from 4k120 8bpc 420 to 4k144 10bpc 444.

Display clock in the DIO case is 1200MHz, but pixel rate is 600MHz
because the pixel format is 420.

Display clock in the HPO case is less (800MHz?) because of ODM combine
which results in a smaller divider.

The DIO is still active in prepare but not active in the optimize which
results in the hang occuring.

During this change there are no planes on the stream so it's safe to
apply the workaround, but dpms_off = false and signal type is not
virtual.

[How]
Check for plane_count == 0, no planes on the stream.

It's easiest to check pipe->plane_state == NULL as an equivalent check
rather than trying to search for the stream status in the context
associated with the stream, so let's do that.

The primary, non MPO pipe should not have a NULL plane state.

Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>