mvebu-gpio: Disable blinking when enabling a GPIO for output

The plat-orion GPIO driver would disable any pin blinking whenever
using a pin for output. Do the same here, as a blinking LED will
continue to blink regardless of what the GPIO pin level is.

Signed-off-by: Jamie Lentin <jm@lentin.co.uk>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>