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.POST b/doc/README.POST
index 0d5e20e..eeb218d 100644
--- a/doc/README.POST
+++ b/doc/README.POST
@@ -713,7 +713,7 @@
 reconfiguration of the physical interface chip.
 
 The test routines for the SCC ethernet tests will be located in
-arch/ppc/cpu/mpc8xx/scc.c.
+arch/powerpc/cpu/mpc8xx/scc.c.
 
 2.2.3.2. UART tests (SMC/SCC)
 
@@ -725,7 +725,7 @@
 test will be executed manually.
 
 The test routine for the SMC/SCC UART tests will be located in
-arch/ppc/cpu/mpc8xx/serial.c.
+arch/powerpc/cpu/mpc8xx/serial.c.
 
 2.2.3.3. USB test