Modify simple_block_yrd condition in nonrd_pickmode for SVC:
allow it to be used also on base temporal_layer, only when
spatial_layer > 1 and block size < 32x32.

Speed up of about ~2% for 3 layer SVC, with little/negligible
loss in quality.

Change-Id: I7734bdae51cf51f22b96f6b2b27da20ea1d84344