pinctrl: mvebu: dove pinctrl driver

This patch adds a SoC specific pinctrl driver for Marvell Dove SoCs
plus DT binding documentation. This driver will use the mvebu pinctrl
driver core.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>