gpio: pl061: Use devm_ioremap_resource()

Use devm_ioremap_resource() in order to make the code simpler.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>