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/board/Marvell/common/ns16550.h b/board/Marvell/common/ns16550.h
index b9691ab..0a2951b 100644
--- a/board/Marvell/common/ns16550.h
+++ b/board/Marvell/common/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)
  * modified slightly to
  * have addresses as offsets from CONFIG_SYS_ISA_BASE
  * added a few more definitions