onclite: Enable AVB and Set BOARD_AVB_ROLLBACK_INDEX.

It encodes PLATFORM_SECURITY_PATCH as the AVB rollback index.

Bug: 78463994
Test: Build with blueline-userdebug. Check the rollback index with
      `avbtool info_image --image $OUT/vbmeta.img`.
Test: Flash and boot into on B1.
Change-Id: Iea02c939d1090e630a36660ea7809273f6724002
Signed-off-by: Dhina17 <dhinalogu@gmail.com>