powerpc: Move include files to arch/powerpc/include/asm

from include/asm-powerpc.  This is the result of a

mkdir arch/powerpc/include/asm
git mv include/asm-powerpc/* arch/powerpc/include/asm

Followed by a few documentation/comment fixups and a couple of places
where <asm-powepc/...> was being used explicitly.  Of the latter only
one was outside the arch code and it is a driver only built for powerpc.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

drivers/infiniband/hw/ehca/ehca_reqs.c

@@ -42,7 +42,7 @@
  */
 
 
-#include <asm-powerpc/system.h>
+#include <asm/system.h>
 #include "ehca_classes.h"
 #include "ehca_tools.h"
 #include "ehca_qes.h"