usb: gadget: fix pxa25x compilation problems

In commit
88f718e3


"ARM: pxa: delete the custom GPIO header"
we removed the implicit inclusion of <mach/gpio.h>
from <linux/gpio.h>.

The pxa25x_udc was not using that, but it was relying
on <linux/gpio.h> to implictly include <mach/gpio.h>
which in turn implicitly included <mach/hardware.h>,
which was needed for the driver to compile.

Fix this up by explicitly including the necessary
<mach/hardware.h> header.

Reported-by: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>