gpio: davinci: convert to use irqdomain support.

Convert the davinci gpio driver to use irqdomain support.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
[grygorii.strashko@ti.com:
 - switch to use one irq-domain per  all GPIO banks
 - keep irq_create_mapping() call in gpio_to_irq_banked() as it
   simply transformed to irq_find_mapping() if IRQ mapping exist
   already]
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>