Currently, we had two gpio chips on cores configured as dual.

This lead to mapping the same memory region twice and duplicating the
init and remove code.

This patch creates a single gpiochip for single and dual cores.
Suggested-by: Alexandre Courbot <gnurou@gmail.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>