MIPS: vmlinux.lds.S: align raw appended dtb to 8 bytes

MIPS: vmlinux.lds.S: align raw appended dtb to 8 bytes

The devicetree specification requires 8-byte alignment in
memory. This is now enforced by libfdt since commit 79edff12060f
("scripts/dtc: Update to upstream version v1.6.0-51-g183df9e9c2b9")
which included the upstream commit 5e735860c478 ("libfdt: Check for
8-byte address alignment in fdt_ro_probe_()").

This broke the MIPS raw appended DTBs which would be appended to
the image immediately following the initramfs section.  This ends
with a 32bit size, resulting in a 4-byte alignment of the DTB.

Fix by padding with zeroes to 8-bytes when MIPS_RAW_APPENDED_DTB
is defined.

Fixes: 79edff12060f ("scripts/dtc: Update to upstream version v1.6.0-51-g183df9e9c2b9")
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>