device_tree: Increase FDT_MAX_SIZE to 1 MiB
    
    It is not uncommon for a contemporary FDT to be larger than 64 KiB,
    leading to failures loading the device tree from sysfs:
    
        qemu-system-aarch64: qemu_fdt_setprop: Couldn't set ...: FDT_ERR_NOSPACE
    
    Hence increase the limit to 1 MiB, like on PPC.
    
    For reference, the largest arm64 DTB created from the Linux sources is
    ca. 75 KiB large (100 KiB when built with symbols/fixup support).
    
    Cc: qemu-stable@nongnu.org
    Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
    Message-id: 1523541337-23919-1-git-send-email-geert+renesas@glider.be
    Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
    Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
    (cherry picked from commit 14ec3cbd7c1e31dca4d23f028100c8f43e156573)
    Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>