Now that we have support for GPIO lines of the SMARC connector, map the
sleep, power and lid switch signals to the corresponding keys using the
gpio-keys and gpio-keys-polled drivers. The power and sleep signals have
dedicated interrupts, thus we use these ones. The lid switch is just
mapped to a GPIO input and needs polling.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>