[ARM] pxa: mmc: add 3rd host controller support for pxa310

This patch is to add the third mmc controller support _only_
for pxa310.

On zylonite, the third controller support one slot.

Signed-off-by: Bridge Wu <bridge.wu@marvell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/mach-pxa/devices.h

@@ -1,5 +1,6 @@
 extern struct platform_device pxa_device_mci;
 extern struct platform_device pxa3xx_device_mci2;
+extern struct platform_device pxa3xx_device_mci3;
 extern struct platform_device pxa_device_udc;
 extern struct platform_device pxa_device_fb;
 extern struct platform_device pxa_device_ffuart;