usb: gadget: atmel_usba: use endian agnostic IO on ARM

Change from using the __raw IO accesors to the endian agnostic versions
of readl/writel_relaxed when not on AVR32. This fixes issues with running
big endian on ARMv7.

Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
--
CC: Nicolas Ferre <nicolas.ferre@atmel.com>
CC: Felipe Balbi <balbi@ti.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: linux-usb@vger.kernel.org
Signed-off-by: Felipe Balbi <balbi@ti.com>