powerpc: ftrace_caller, _mcount is exported to modules so needs _GLOBAL_TOC()

When testing the ftrace function tracer, I realised that ftrace_caller
and mcount are called from modules and they both call into C, therefore
they need the ABIv2 global entry point to establish r2.
Signed-off-by: Anton Blanchard <anton@samba.org>

arch/powerpc/kernel/entry_64.S

@@ -1175,7 +1175,7 @@ _GLOBAL(mcount)
 _GLOBAL(_mcount)
 	blr
 
-_GLOBAL(ftrace_caller)
+_GLOBAL_TOC(ftrace_caller)
 	/* Taken from output of objdump from lib64/glibc */
 	mflr	r3
 	ld	r11, 0(r1)
@@ -1199,10 +1199,7 @@ _GLOBAL(ftrace_graph_stub)
 _GLOBAL(ftrace_stub)
 	blr
 #else
-_GLOBAL(mcount)
-	blr
-
-_GLOBAL(_mcount)
+_GLOBAL_TOC(_mcount)
 	/* Taken from output of objdump from lib64/glibc */
 	mflr	r3
 	ld	r11, 0(r1)