MIPS: kexec: Fix random crashes while loading crashkernel

Fixed compilation errors in case of non-KEXEC kernel
Rearranging code so that crashk_res gets updated.
- crashk_res is updated after mips_parse_crashkernel(),
   after resource_init(), which is after arch_mem_init().
- The reserved memory is actually treated as Usable memory,
   Unless we load the crash kernel, everything works.

Signed-off-by: Prem Mallappa <pmallappa@caviumnetworks.com>
Cc: linux-mips <linux-mips@linux-mips.org>
Patchwork: http://patchwork.linux-mips.org/patch/5805/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>