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
Bug: 427113482
Test: Manual
Flag: EXEMPT bugfix
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:ba571df05a6e65545dbda4c9988c2bc23aae8f16)
Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:25c66cbc720dd6c28aa1abe32eecda1ea4878328
Merged-In: I829e2cc4da755a713c6d0994771fc269d47bbbb5
Change-Id: I829e2cc4da755a713c6d0994771fc269d47bbbb5