wakeup: Add last wake up source logging for suspend abort reason.

wakeup: Add last wake up source logging for suspend abort reason.

There is a possibility that a wakeup source event is received after
the device prepares to suspend which might cause the suspend to abort.

This patch adds the functionality of reporting the last active wakeup
source which is currently not active but caused the suspend to abort reason
via the /sys/kernel/power/last_wakeup_reason file.

Change-Id: I1760d462f497b33e425f5565cb6cff5973932ec3
Signed-off-by: Ruchi Kandoi <kandoiruchi@google.com>