x86, mm: fault.c, simplify kmmio_fault()

Impact: cleanup

Remove an #ifdef from kmmio_fault() - we can do this by
providing default implementations for is_kmmio_active()
and kmmio_handler(). The compiler optimizes it all away
in the !CONFIG_MMIOTRACE case.

Also, while at it, clean up mmiotrace.h a bit:

 - standard header guards
 - standard vertical spaces for structure definitions

No code changed (both with mmiotrace on and off in the config):

   text	   data	    bss	    dec	    hex	filename
   2947	     12	     12	   2971	    b9b	fault.o.before
   2947	     12	     12	   2971	    b9b	fault.o.after

Cc: Pekka Paalanen <pq@iki.fi>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 3e366146..fe99af4 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -55,13 +55,14 @@
 	PF_INSTR	=		1 << 4,
 };
 
+/*
+ * (returns 0 if mmiotrace is disabled)
+ */
 static inline int kmmio_fault(struct pt_regs *regs, unsigned long addr)
 {
-#ifdef CONFIG_MMIOTRACE
 	if (unlikely(is_kmmio_active()))
 		if (kmmio_handler(regs, addr) == 1)
 			return -1;
-#endif
 	return 0;
 }