ipq807x: prpl-haze: fix sysupgrade flashing from bootloader

ipq807x: prpl-haze: fix sysupgrade flashing from bootloader

While flashing sysupgrade image from U-Boot, then the rootfs_data
overlay filesystem formatting is left for the fstools during firstboot,
but that wont work as mkfs.f2fs is missing in the sysupgrade image:

 mount_root: overlay filesystem in /dev/loop0 has not been formatted yet
 mount_root: no usable overlay filesystem found, using tmpfs overlay
 sh: mkfs.f2fs: not found

 Filesystem                Size      Used Available Use% Mounted on
 /dev/loop0              139.6M     46.9M     92.6M  34% /overlay

 Number  Start (sector)    End (sector)  Size       Code  Name
  20           98850          406349   150.1 MiB   FFFF  rootfs

So lets fix it by adding f2fs support to the sysupgrade image.

Signed-off-by: Petr Štetiar <ynezz@true.cz>