arch: add missing prepare_ftrace_return() prototypes

The prototype for prepare_ftrace_return() is architecture specific and
can't be in a global header. Since it's normally called from assembly,
it doesn't really need a prototype, but we get a warning if it's missing:

arch/csky/kernel/ftrace.c:147:6: error: no previous prototype for 'prepare_ftrace_return' [-Werror=missing-prototypes]
arch/microblaze/kernel/ftrace.c:22:6: error: no previous prototype for 'prepare_ftrace_return' [-Werror=missing-prototypes]
arch/mips/kernel/ftrace.c:305:6: error: no previous prototype for 'prepare_ftrace_return' [-Werror=missing-prototypes]

Add the prototypes for the three architectures that don't already have
one in asm/ftrace.h.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/csky/include/asm/ftrace.h

@@ -26,5 +26,9 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 
 struct dyn_arch_ftrace {
 };
+
+void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
+			   unsigned long frame_pointer);
+
 #endif /* !__ASSEMBLY__ */
 #endif /* __ASM_CSKY_FTRACE_H */

arch/microblaze/include/asm/ftrace.h

@@ -10,6 +10,7 @@
 #ifndef __ASSEMBLY__
 extern void _mcount(void);
 extern void ftrace_call_graph(void);
+void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr);
 #endif
 
 #ifdef CONFIG_DYNAMIC_FTRACE

arch/mips/include/asm/ftrace.h

@@ -85,6 +85,10 @@ struct dyn_arch_ftrace {
 };
 
 #endif /*  CONFIG_DYNAMIC_FTRACE */
+
+void prepare_ftrace_return(unsigned long *parent_ra_addr, unsigned long self_ra,
+			   unsigned long fp);
+
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_FUNCTION_TRACER */
 #endif /* _ASM_MIPS_FTRACE_H */