Refrain from using the custom gpio_line_get() to read the power
key on the N2100, use the gpiolib function gpio_get() instead.
Also request the line in the GPIOs initicall, and move the poll
timer setup to that inicall so the gpio chip is available before
we request this GPIO and start to poll it.

Cc: Lennert Buytenhek <kernel@wantstofly.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Mikael Pettersson <mikpe@it.uu.se>
Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>