gpio: davinci: Remove custom .xlate

With the current redesign of driver it's not necessary to have
custom .xlate() as the gpiolib will assign default of_gpio_simple_xlate().

Suggested-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>