gpio: lpc32xx: allow building on non-lpc32xx targets

The driver uses hardwire MMIO addresses instead of the data
that is passed in device tree. Change it over to only
hardcode the register offset values and allow compile-testing.

Acked-by: Sylvain Lemieux <slemieux.tyco@gmail.com>
Tested-by: Sylvain Lemieux <slemieux.tyco@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>