mvebu: pinctrl: Add Armada 38x driver

This new Armada 38x driver is based on Linux kernel driver. It can set any
pin to any valid function specified in DT like Linux kernel, it provides
support for 'pinmux status -a' command and also for pinctrl_gpio_request().

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>