MPC8xxx: Define cache ops for USB

This patch conditionally defines flush_dcache_range() and
invalidate_dcache_range() on MPC8xxx, to avoid EHCI complaining,
resulting in the following output:

$ ARCH=powerpc CROSS_COMPILE=powerpc-linux-gnu- ./MAKEALL MPC8572DS
Configuring for MPC8572DS board...
make: *** [u-boot] Error 1
powerpc-linux-gnu-size: './u-boot': No such file
e1000.c: In function ‘e1000_initialize’:
e1000.c:5264:13: warning: assignment from incompatible pointer type [enabled by default]
tsec.c: In function ‘tsec_initialize’:
tsec.c:638:12: warning: assignment from incompatible pointer type [enabled by default]
drivers/usb/host/libusb_host.o: In function `ehci_td_buffer':
/home/marex/U-Boot/u-boot-imx/drivers/usb/host/ehci-hcd.c:186: undefined reference to `flush_dcache_range'
drivers/usb/host/libusb_host.o: In function `ehci_submit_async':
/home/marex/U-Boot/u-boot-imx/drivers/usb/host/ehci-hcd.c:346: undefined reference to `flush_dcache_range'
/home/marex/U-Boot/u-boot-imx/drivers/usb/host/ehci-hcd.c:348: undefined reference to `flush_dcache_range'
/home/marex/U-Boot/u-boot-imx/drivers/usb/host/ehci-hcd.c:349: undefined reference to `flush_dcache_range'
/home/marex/U-Boot/u-boot-imx/drivers/usb/host/ehci-hcd.c:372: undefined reference to `invalidate_dcache_range'
/home/marex/U-Boot/u-boot-imx/drivers/usb/host/ehci-hcd.c:374: undefined reference to `invalidate_dcache_range'
/home/marex/U-Boot/u-boot-imx/drivers/usb/host/ehci-hcd.c:376: undefined reference to `invalidate_dcache_range'
/home/marex/U-Boot/u-boot-imx/drivers/usb/host/ehci-hcd.c:386: undefined reference to `invalidate_dcache_range'
make: *** [u-boot] Error 1

--------------------- SUMMARY ----------------------------
Boards compiled: 1
Boards with errors: 1 ( MPC8572DS )
----------------------------------------------------------

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Anatolij Gustschin <agust@denx.de>
diff --git a/arch/powerpc/cpu/mpc83xx/cache.c b/arch/powerpc/cpu/mpc83xx/cache.c
new file mode 100644
index 0000000..2a08b65
--- /dev/null
+++ b/arch/powerpc/cpu/mpc83xx/cache.c
@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2012 Marek Vasut <marex@denx.de>
+ *
+ * This file contains stub implementation of
+ *   invalidate_dcache_range()
+ *   flush_dcache_range()
+ *
+ * See file CREDITS for list of people who contributed to this
+ * project.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+ * MA 02111-1307 USA
+ */
+
+void invalidate_dcache_range(unsigned long start, unsigned long stop)
+{
+}
+
+void flush_dcache_range(unsigned long start, unsigned long stop)
+{
+}