fs_mgr: remount: add -R argument

The -R flag tells remount it can reboot to disable verity or to
run fsck on an ext4 deduped filesystem, or both.

Testing may include a manual component because adb-remount-test.sh
needs to run from a device in an enable-verity state to test this.

Only recognizes chained avb.

Test: adb-remount-test.sh
Bug: 122602260
Change-Id: I6ce4372532d9b933dcca9e2bec544d525b76c4d9