MIPS: kexec: Do not reserve invalid crashkernel memory on boot

MIPS: kexec: Do not reserve invalid crashkernel memory on boot

Do not reserve memory for the crashkernel if the commandline argument
points to a wrong location. This can happen if the location is specified
wrong or if the same commandline is reused when starting the crashkernel
- in the latter case the reserved memory would point to the location
from which the crashkernel is executing.

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14612/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>