move arm boot partition to ext3
    
    With e2fsprogs after 1.43 the 64bit and metadata_csum features are
    enabled by default. These features are not currently supported in
    u-boot and the 64bit feature introduces changes such that it cannot
    be read by implementations that do not support it. U-Boot does not
    support the functionality and hence now won't mount it just in case
    it corrupts the filesystem, which is a reasonable response, this how
    ever stops us from booting when we have a ext4 /boot file system
    which means basically we end up with a pot plant. Go back to using
    ext3 for the time being as the mkfs.ext3 option doesn't enable these
    features and we get booting systems!! YAY \o/