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/doc/README.RPXlite b/doc/README.RPXlite
index 0aa4d11..3ca6711 100644
--- a/doc/README.RPXlite
+++ b/doc/README.RPXlite
@@ -116,7 +116,7 @@
 	board/RPXLITE/RPXLITE.c		/* DRAM-related routines */
 	board/RPXLITE/flash.c		/* flash-related routines */
 	board/RPXLITE/config.mk		/* set text base address */
-	arch/ppc/cpu/mpc8xx/serial.c			/* board specific register setting */
+	arch/powerpc/cpu/mpc8xx/serial.c /* board specific register setting */
 	include/config_RPXLITE.h	/* board specific registers */
 
 	See 'reg_config.txt' for register values in detail.