OMAP/gpio: drop MPUIO static base

The OMAP GPIO driver hardcodes the MPIO chip base, but there
is no point: we have already moved all consumers over to using
descriptor look-ups.

Drop the MPUIO GPIO base and use dynamic assignment.

Root out the unused instances of the OMAP_MPUIO() macro and
delete the unused OMAP_GPIO_IS_MPUIO() macro.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Tested-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>