Revert "bcm2708: fix gpio_to_irq() name clash"

This reverts commit dee3db1c55e9a1c2efce858f44d9810cc2392b18.

Conflicts:
	arch/arm/mach-bcm2708/bcm2708_gpio.c
bcm2708: select NEED_MACH_GPIO_H

makers out there use to use gpio_to_irq() in board setup code. it is
necessary that gpio_to_irq() be defined as a macro for this to work.

https://github.com/raspberrypi/linux/commit/01464226ac6089bd6a33f9899cc792c2355ebf39,
on its way towards devicetree, introduces a switch NEED_MACH_GPIO_H
that platforms have to set to get the macro definition of
gpio_to_irq() - otherwise, the gpiolib incarnation of gpio_to_irq() is
found instead which does not work from board code.

define NEED_MACH_GPIO_H to make things work again without any pain for
makers (though this clearly is in the way of devicetree).
Merge pull request #505 from jfasch/rpi-3.10.y-fix-gpio_to_irq

Please pull: NEED_MACH_GPIO_H vs. gpio_to_irq() woes