gpio: davinci: Remove gpio2regs function

gpio2regs is written making an assumption that driver supports only
one instance of gpio controller. Removing this and adding a generic
array so as to support multiple instances of gpio controllers.

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>