irq_to_gpio support

[Richard Zhao]

Hi Grant & Linus

I saw gpio lib didn't provide irq_to_gpio support. Are we dropping it?
git grep irq_to_gpio still return a lot of things.

I'm looking at drivers/input/touchscreen/egalax_ts.c driver.
It failed to compile without irq_to_gpio. It's a i2c client device and
use irq line configured as gpio to wakeup touchscreen controller.
If we don't have irq_to_gpio, I'm afraid it has to use plat data or
of property to pass gpio number.

Thanks
Richard