vp9-svc: Fix to frames_since_golden update for SVC.

vp9-svc: Fix to frames_since_golden update for SVC.

When the second (gf) temporal reference is used in SVC:
the reference is refreshed on base TL superframes, and so
the rc->frames_since_golden counter was also only updated on
base TL frames. But this was disabling the golden reference
from being used as a temporal reference for TL > 0 frames
(since frames_since_golden was 0/not updated on TL > 0 frames).

Fix is to copy the update of rc->frames_since_golden to all
upper temporal layers. This allows TL > 0 frames to test the
golden inter mode.

Gain on RTC set: ~2%, ~8% on desktop_vga clip.
Encode time increase ~5-8% on linux, 3SL-3TL run with 1 thread.

For now keep this off for TL > 0 frames in speed features, so
this change does not change current behavior for speed >= 7.

Change-Id: I405708f3f80039ae47bd64ec53e66f92160acd9e