libvpx

Add cyclic refresh parameters to svc-layer context.

For 1 pass CBR spatial-SVC:
Add cyclic refresh parameters to the svc-layer context.

This allows cyclic refresh (aq-mode=3) to be applied to
the whole super-frame (all spatial layers).
This gives a performance improvement for spatial layer encoding.

Addd the aq_mode mode on/off setting as command line option.

Change-Id: Ib9c3b5ba3cb7851bfb8c37d4f911664bef38e165