pinctrl: mvebu: provide per-control private data

Provide per-control private data into each mvebu pinctrl method, which
will allow us to provide some completely generic helpers without the
global variable and per-instance function definitions that would be
required when we have multiple pin controllers on a SoC.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>