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/amcc/sequoia/sdram.c b/board/amcc/sequoia/sdram.c
index b5c7d6d..cabeceb 100644
--- a/board/amcc/sequoia/sdram.c
+++ b/board/amcc/sequoia/sdram.c
@@ -40,7 +40,7 @@
 extern void denali_core_search_data_eye(void);
 
 #if defined(CONFIG_NAND_SPL)
-/* Using arch/ppc/cpu/ppc4xx/speed.c to calculate the bus frequency is too big
+/* Using arch/powerpc/cpu/ppc4xx/speed.c to calculate the bus frequency is too big
  * for the 4k NAND boot image so define bus_frequency to 133MHz here
  * which is save for the refresh counter setup.
  */