amd/dc/dce100: On dce100, set clocks to 0 on suspend

[Why]
When a dce100 asic was suspended, the clocks were not set to 0.
Upon resume, the new clock was compared to the existing clock,
they were found to be the same, and so the clock was not set.
This resulted in a pernicious blackscreen.

[How]
In atomic commit, check to see if there are any active pipes.
If no, set clocks to 0

Signed-off-by: David Francis <David.Francis@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>