sh: Add MMU dependency for kexec

Kexec is not likely to work on NON-MMU CPU because this added
depend on MMU for kexec.
Signed-off-by: NNobuhiro Iwamatsu <iwamatsu.nobuhiro@renesas.com>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>

arch/sh/Kconfig

@@ -530,7 +530,7 @@ source kernel/Kconfig.hz
 
 config KEXEC
 	bool "kexec system call (EXPERIMENTAL)"
-	depends on SUPERH32 && EXPERIMENTAL
+	depends on SUPERH32 && EXPERIMENTAL && MMU
 	help
 	  kexec is a system call that implements the ability to shutdown your
 	  current kernel, and to start another kernel.  It is like a reboot