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/sixnet/u-boot.lds b/board/sixnet/u-boot.lds
index c3e7f50..43a8e20 100644
--- a/board/sixnet/u-boot.lds
+++ b/board/sixnet/u-boot.lds
@@ -52,7 +52,7 @@
   .plt : { *(.plt) }
   .text      :
   {
-    arch/ppc/cpu/mpc8xx/start.o	(.text)
+    arch/powerpc/cpu/mpc8xx/start.o	(.text)
     common/env_embedded.o(.text)
     *(.text)
     *(.got1)