Move arch/ppc to arch/powerpc

As discussed on the list, move "arch/ppc" to "arch/powerpc" to
better match the Linux directory structure.

Please note that this patch also changes the "ppc" target in
MAKEALL to "powerpc" to match this new infrastructure. But "ppc"
is kept as an alias for now, to not break compatibility with
scripts using this name.

Signed-off-by: Stefan Roese <sr@denx.de>
Acked-by: Wolfgang Denk <wd@denx.de>
Acked-by: Detlev Zundel <dzu@denx.de>
Acked-by: Kim Phillips <kim.phillips@freescale.com>
Cc: Peter Tyser <ptyser@xes-inc.com>
Cc: Anatolij Gustschin <agust@denx.de>
diff --git a/include/ns16550.h b/include/ns16550.h
index ce606b5..9ea81e9 100644
--- a/include/ns16550.h
+++ b/include/ns16550.h
@@ -1,6 +1,6 @@
 /*
  * NS16550 Serial Port
- * originally from linux source (arch/ppc/boot/ns16550.h)
+ * originally from linux source (arch/powerpc/boot/ns16550.h)
  *
  * Cleanup and unification
  * (C) 2009 by Detlev Zundel, DENX Software Engineering GmbH