[ARM] 3958/1: add platform device (pxa2xx-udc)to ixp4xx

Create include/asm-arm/arch-ixp4xx/udc.h and
add platfrom device ixp4xx_udc_device into
arch/arm/mach-ixp4xx/common.c.

This allows us to use pxa2xx-udc on
the ixp4xx platfrom. Both pxa2xx and
ixp4xx use the same device controller.

Signed-off-by: Milan Svoboda <msvoboda@ra.rockwell.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>