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/keymile/common/keymile_hdlc_enet.c b/board/keymile/common/keymile_hdlc_enet.c
index ceddaf7..ce5e4d6 100644
--- a/board/keymile/common/keymile_hdlc_enet.c
+++ b/board/keymile/common/keymile_hdlc_enet.c
@@ -2,7 +2,7 @@
  * (C) Copyright 2008
  * Gary Jennejohn, DENX Software Engineering GmbH, garyj@denx.de.
  *
- * Based in part on arch/ppc/cpu/mpc8260/ether_scc.c.
+ * Based in part on arch/powerpc/cpu/mpc8260/ether_scc.c.
  *
  * See file CREDITS for list of people who contributed to this
  * project.