sh: Add missing asm/ftrace.h.

This was missed with the ftrace support commit.. check it in now.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/ftrace.h

+#ifndef __ASM_SH_FTRACE_H
+#define __ASM_SH_FTRACE_H
+
+#ifndef __ASSEMBLY__
+extern void mcount(void);
+#endif
+
+#endif /* __ASM_SH_FTRACE_H */