sh: fix up CONFIG_KEXEC=n build.

The reserve_crashkernel() definition is in asm/kexec.h which is only
dragged in via linux/kexec.h if CONFIG_KEXEC is set. Just switch over to
asm/kexec.h unconditionally to fix up the build.
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/mm/init.c

@@ -17,10 +17,10 @@
 #include <linux/percpu.h>
 #include <linux/io.h>
 #include <linux/lmb.h>
-#include <linux/kexec.h>
 #include <linux/dma-mapping.h>
 #include <asm/mmu_context.h>
 #include <asm/mmzone.h>
+#include <asm/kexec.h>
 #include <asm/tlb.h>
 #include <asm/cacheflush.h>
 #include <asm/sections.h>