C2SoftDav1dDec: configure decoder to output only one layer in SVC mode

dav1d default settings are configured to output all layers for svc
clips. The plugin is not designed to handle this. Disable outputting all
layers buffers

Bug: 424384335
Test: Manual
Flag: EXEMPT bugfix
Change-Id: I829e2cc4da755a713c6d0994771fc269d47bbbb5