vp9-svc: Update layer_id of frame buffer idx last refreshed.

vp9-svc: Update layer_id of frame buffer idx last refreshed.

Remove some unused code and add parameter to keep track
of the layer_id of the frame buffer indices last refreshed.

This is useful for verifying constaints on spatial-temporal pattern,
for fixed/non-flexible mode.

Change-Id: I6957bb43157eb31df49dac1b8245facc043e4a49