pinctrl: mvebu: switch drivers to generic simple mmio

Move the mvebu pinctrl drivers over to the generic simple mmio
implementation, saving a substantial number of lines of code in
the process.

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