libre: uboot4extlinux-sunxi: workaround linter issues on ppc64le
    
    When running parabola-repolint[1] for ppc64le, there is the
    following error or warning:
        unhandled SRCINFO key: "makedepends_ppc64le"
        (makedepends_ppc64le = arm-none-eabi-gcc)
    
    As ppc64le is still experimental, we can safely remove it from
    the supported architectures in this PKGBUILD to avoid creating
    too much noise for the people working on the ppc64le port of
    Parabola.
    
    This is a real concern as oaken-source, who run this
    parabola-repolint had that issue and discussed with me about
    it on the #parabola IRC channel on liberachat.
    
    [1]https://git.parabola.nu/~oaken-source/parabola-repolint.git/
    
    Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>