linux-phytec-ti

gpio: generic: support input-only chips

Allow chips to indicates that they are input-only and thus cannot set
the output value.  This will be used by the gpio-etraxfs driver.

Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>