gpio: mxc: use devm_platform_ioremap_resource() to simplify code

Use the new helper devm_platform_ioremap_resource() which wraps the
platform_get_resource() and devm_ioremap_resource() together, to
simplify the code.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>