Many of the gpio_to_irq implementations use the gpiolib version of this
function.  Provide the standard gpiolib gpio_to_irq() for everyone, but
allow platforms to override it if they wish.  Add the neccessary
overrides for those platforms which do not use the standard definition.

Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>