Mount fs from /etc/fstab.overlay only if overlayfs supported

board/common/overlay/etc/fstab.disk

@@ -1,4 +1,3 @@
 # <file system> <mount pt>            <type>   <options>         <dump> <pass>
 /dev/mmcblk0p1  /boot                 vfat     ro,defaults       0      0
 /dev/mmcblk0p3  /data                 ext4     defaults,noatime  0      0
-overlay         /usr                  overlay  lowerdir=/usr,upperdir=/data/usr,workdir=/data/.overlay 0 0

board/common/overlay/etc/fstab.overlay

@@ -0,0 +1,2 @@
+# <file system> <mount pt>            <type>   <options>                                                        <dump> <pass>
+overlay         /usr                  overlay  lowerdir=/usr,upperdir=/data/usr,workdir=/data/.overlay-usr      0 0

board/common/overlay/etc/init.d/S01mountall

@@ -6,6 +6,7 @@ mount_fs() {
     msg_begin "Mounting filesystems"
     /bin/mount -T /etc/fstab.disk -a &&
     /bin/mount -T /etc/fstab.extra -a &&
+    if grep -qw overlay /proc/filesystems; then /bin/mount -T /data/etc/fstab.overlay -a; fi &&
     if [[ -r /data/etc/fstab.user ]]; then /bin/mount -T /data/etc/fstab.user -a; fi
 
     test $? == 0 && msg_done || msg_fail