powerpc: clean up after powermac build merge

Complete moving arch/ppc64/kernel/mpic.h,
        include/asm-ppc/reg.h, include/asm-ppc64/kdebug.h
	        and include/asm-ppc64/kprobes.h
Add arch/powerpc/platforms/Makefile and use it from
	arch/powerpc/Makefile
Introduce OLDARCH temporarily so we can point back to
	the originating architecture

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
diff --git a/include/asm-powerpc/system.h b/include/asm-powerpc/system.h
index be542ef..1b64879 100644
--- a/include/asm-powerpc/system.h
+++ b/include/asm-powerpc/system.h
@@ -1,8 +1,8 @@
 /*
  * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
  */
-#ifndef __PPC_SYSTEM_H
-#define __PPC_SYSTEM_H
+#ifndef _ASM_POWERPC_SYSTEM_H
+#define _ASM_POWERPC_SYSTEM_H
 
 #include <linux/config.h>
 #include <linux/kernel.h>
@@ -347,4 +347,4 @@
 #define arch_align_stack(x) (x)
 
 #endif /* __KERNEL__ */
-#endif /* __PPC_SYSTEM_H */
+#endif /* _ASM_POWERPC_SYSTEM_H */