MIPS: generic/kexec: add support for a DTB passed in a separate buffer

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14615/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>