gpio: ich: add GPO_BLINK support

This patch makes sure blink hardware is disabled for selected GPIO. Blink
hardware is controled by GPO_BLINK register and is available for GPIOs from 0
to 31.

Signed-off-by: Vincent Donnefort <vdonnefort@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>