gpio: davinci: Add support for multiple GPIO controllers

Update GPIO driver to support Multiple GPIO controllers by updating
the base of subsequent GPIO chips with total of previous chips
gpio count so that gpio_add_chip gets unique numbers.

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>