pxa2xx_udc: cleanups, use platform_get_irq

Make the pxa2xx_udc driver fetch its IRQ from platform resources
rather than using compile-time constants, so that it works properly
on IXP4xx systems not just PXA21x/25x/26x.

Other updates:
 - Do that using platform_get_irq()
 - Switch to platform_driver_probe()
 - Handle device_add() errors
 - Remove "function" sysfs attribute and its potential errors
 - Whitespace cleanups

Signed-off-by: Milan Svoboda <msvoboda@ra.rockwell.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>