MIPS: boot/compressed: Copy DTB to aligned address

Since 5.12-rc1, the Device Tree blob must now be properly aligned.

Therefore, the decompress routine must be careful to copy the blob at
the next aligned address after the kernel image.

This commit fixes the kernel sometimes not booting with a Device Tree
blob appended to it.

Fixes: 79edff12 ("scripts/dtc: Update to upstream version v1.6.0-51-g183df9e9c2b9")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>