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>