drm/amd/display: Flip pending check timeout due to disabled hubp

[Why]
When pipe locks are being taken we wait for flip pending to clear first.
In some cases the pipe mapping is changed and the pending we're checking
for will never clear.

[How]
Don't check disabled pipes for flip pending.

Signed-off-by: Aric Cyr <aric.cyr@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>