power_supply: Prevent suspend until power supply events are processed

power_supply: Prevent suspend until power supply events are processed

This patch, originally authored by Arve Hjonnevag and Todd Poynor,
prevents the system from entering suspend mode until the power supply
plug, unplug, or any other change of state event is fully processed. This
guarantees that the screen lights up and displays the battery charging
state. The implementation uses the power supply wakeup_source object.

Change-Id: I541e6a5d0567f2a731f14abc16fda30256ae93fe
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Arve Hjonnevag <arve@android.com>
Cc: Todd Poynor <toddpoynor@google.com>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Zoran Markovic <zoran.markovic@linaro.org>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>