powerpc, 5xxx, 512x: remove support for mpc5xxx and mpc512x

There was for long time no activity in the mpx5xxx area.
We need to go further and convert to Kconfig, but it
turned out, nobody is interested anymore in mpc5xxx,
so remove it.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/doc/README.generic_usb_ohci b/doc/README.generic_usb_ohci
index ba7cea8..61300c3 100644
--- a/doc/README.generic_usb_ohci
+++ b/doc/README.generic_usb_ohci
@@ -36,8 +36,8 @@
 ------------------
 
 The USB bus operates in little endian, but unfortunately there are
-OHCI controllers that operate in big endian such as ppc4xx and
-mpc5xxx. For these the config option
+OHCI controllers that operate in big endian such as ppc4xx. For these the
+config option
 
 	CONFIG_SYS_OHCI_BE_CONTROLLER