power: wakeup_reason: send uevent to user space

Sends uevent to user space when enter or out of suspend,
the modules of user space can use it to do some necessary
operation. For example, in order to reduce power consumption,
we can use this mechanism to send instructions which can
reduce unnecessary wake-up sources of modem to modem driver.
Any module except modem can also monitor this event for power
consumption purpose.

Change-Id: I62ca3ed02ea78e06735355a2c8b6d515e36dc7e6
Signed-off-by: xianzhu <xianzhu@codeaurora.org>