pinctrl: mvebu: new driver for Orion platforms

This commit extends the pinctrl mvebu logic with a new driver to cover
Orion5x SoC. It supports the definitions for the 5181l, 5182 and 5281
variants of Orion5x, which are the three ones supported by the old
style MPP code in arch/arm/mach-orion5x/.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>