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/luan/luan.c b/board/amcc/luan/luan.c
index 6542565..4e12e9a 100644
--- a/board/amcc/luan/luan.c
+++ b/board/amcc/luan/luan.c
@@ -119,7 +119,7 @@
 }
 
 /*
- * Override the default functions in arch/ppc/cpu/ppc4xx/44x_spd_ddr2.c with
+ * Override the default functions in arch/powerpc/cpu/ppc4xx/44x_spd_ddr2.c with
  * board specific values.
  */
 u32 ddr_clktr(u32 default_val) {