drm/amd/display: fix report display count logic

[Why]
Previous logic to update display count in commit_planes_do_stream_update
doesn't cover all cases.

[How]
Update display count as part of clock updates. Count virtual stream
as active to work around headless situation.

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>