pinctrl: armada-37xx: Make use of the devm_platform_ioremap_resource()

Use the devm_platform_ioremap_resource() helper instead of
calling of_address_to_resource() and devm_ioremap_resource()
separately.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Gregory CLEMENT <gregory.clement@bootlin.com>