codec2: Add support for B frames in C2SoftAvcEnc plugin

Test: VtsHidlC2V1_0TargetVideoEncTest -I software -C c2.android.avc.encoder -P /sdcard/res/

Bug: 122593474

Change-Id: Id9b40accd4185183e12e20e9dea5e88e8295fae0
2 files changed