vp9-rtc: Fix to rate cost for switchable filter

Add consistent switchable rate cost, which should be only
when non-integer motion mode is tested.

Neutal/negligible change in metrics.

Also diable the re-evaluation of ZEROMV mode after denoising
feature, as this rate cost fix exposed an exsting issue
with this feature.

Change-Id: I9e5479281810a392b9a409e238c564b2def8e546
1 file changed