fs_mgr: Add fs_mgr_overlayfs_required_devices()

Added fs_mgr_overlayfs_required_devices() as hint to init to make sure
the device gets created before fs_mgr_overlayfs_mount_all().

Test: manual
Bug: 109821005
Change-Id: Iab038f3e0252a357b082bb08db3679512b9badec
3 files changed