gpio-button-hotplug: add KEY_POWER2 handling

gpio-button-hotplug: add KEY_POWER2 handling

For devices such as BTHOMEHUBV5A with both reset and restart buttons,
its easily accessible restart button has been assigned to KEY_POWER
power script to poweroff preventing accidental (or malicious) factory
resets by KEY_RESTART reset script. However an easily accessible button
immediately powering off the device is also undesirable.

As KEY_RESTART is already used for reset script (and there's no
KEY_REBOOT in Linux input events), use KEY_POWER2 for rebooting via new
reboot script with 5 second seen delay.

Fixes: FS#1965
Signed-off-by: Alan Swanson <reiver@improbability.net>
Signed-off-by: Petr Štetiar <ynezz@true.cz> [long line wrap]