perf: Always build the powerpc perf_arch_fetch_caller_regs version

Now that software events use perf_arch_fetch_caller_regs() too, we
need the powerpc version to be always built.

Fixes the following build error:

	(.text+0x3210): undefined reference to `perf_arch_fetch_caller_regs'
	(.text+0x3324): undefined reference to `perf_arch_fetch_caller_regs'
	(.text+0x33bc): undefined reference to `perf_arch_fetch_caller_regs'
	(.text+0x33ec): undefined reference to `perf_arch_fetch_caller_regs'
	(.text+0xd4a0): undefined reference to `perf_arch_fetch_caller_regs'
	arch/powerpc/kernel/built-in.o:(.text+0xd528): more undefined references to `perf_arch_fetch_caller_regs' follow
	make[1]: *** [.tmp_vmlinux1] Error 1
	make: *** [sub-make] Error 2

Reported-by: Michael Ellerman <michael@ellerman.id.au>
Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/misc.S

@@ -128,7 +128,6 @@ _GLOBAL(__restore_cpu_power7)
 	/* place holder */
 	blr
 
-#ifdef CONFIG_EVENT_TRACING
 /*
  * Get a minimal set of registers for our caller's nth caller.
  * r3 = regs pointer, r5 = n.
@@ -154,4 +153,3 @@ _GLOBAL(perf_arch_fetch_caller_regs)
 	PPC_STL	r4,_NIP-STACK_FRAME_OVERHEAD(r3)
 	PPC_STL	r7,_LINK-STACK_FRAME_OVERHEAD(r3)
 	blr
-#endif /* CONFIG_EVENT_TRACING */