vp9-svc: Hybrid search on spatial layers whose base is key.

vp9-svc: Hybrid search on spatial layers whose base is key.

For spatial layers whose base is a key frame, i.e., when
svc.layer_context[cpi->svc.temporal_layer_id].is_key_frame = 1,
allow for hybrid search, similar to what we do on key frames.

For small blocks (<= 8x8) rd-based intra search will be used,
otherwise non-rd pick mode is used.

Feature is controlled by nonrd_keyframe, which is set to 1
for now on non-base spatial layers, so this change has
currently no effect.

Small change only when inter-layer prediction is off, as we now
call vp9_pick_intra_mode instead of vp9_pick_inter_mode on key frame.
But this change is very small/insignificant.

Change-Id: I5372470f720812926ebbe6c4ce68c04336ce0bdd