vp9-svc: Update to SET/GET_SVC_REF_FRAME_CONFIG api

Add update_buffer_slot to SVC API to allow for refreshing
any of the 8 reference buffers. Remove frame_flags from
the struct.

Remove svc tests from vp8 build.

BUG=b/112292577
Change-Id: I0551c349d2b311227245a8ed1639cdbbaf5bc5db
9 files changed