For SVC 1 pass real-time: add condition to skip the
golden (spatial) reference mode in non-rd pickmode.
Condition is to skip golden if the sse of zeromv-last mode
is below threshold. And change order in ref_mode_set_svc
to make sure golden zeromv is tested after last-nearest.

Speedup ~3-4% with little/negligible quality loss.

Change-Id: I6cbe314a93210454ba2997945f714015f1b2fca3