Improve the documentation to clarify level vs edge triggered power off.
Improve the comments for level vs edge triggered power off.
Make use of gpio_is_valid().
Reported-by: NStephen Warren <swarren@wwwdotorg.org>
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Signed-off-by: NJason Cooper <jason@lakedaemon.net>