ANDROID: power: wakeup_reason: add an API to log wakeup reasons

Add API log_wakeup_reason() and expose it to userspace via sysfs path
/sys/kernel/wakeup_reasons/last_resume_reason

Bug: 120445600
Signed-off-by: Ruchi Kandoi <kandoiruchi@google.com>
[AmitP: Folded following android-4.9 commit changes into this patch
        1135122a192a ("ANDROID: POWER: fix compile warnings in log_wakeup_reason")
        b4e6247778b0 ("ANDROID: Power: Changes the permission to read only for sysfs file /sys/kernel/wakeup_reasons/last_resume_reason")
        e13dbc7c69cd ("ANDROID: power: wakeup_reason: rename irq_count to irqcount")]
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
[astrachan: Folded the following changes into this patch:
            39d7c7fe91c0 ("ANDROID: power: wakeup_reason: Add guard condition for maximum wakeup reasons")
            0730434bdf49 ("ANDROID: power: wakeup_reason: Avoids bogus error messages for the suspend aborts.")
            4e42dceae54e ("ANDROID: power: wakeup_reason: Adds functionality to log the last suspend abort reason.")
            f21313b70ac7 ("ANDROID: power: wakeup_reason: Report suspend times from last_suspend_time")
            f97ec34442ac ("ANDROID: power: wakeup_reason: fix suspend time reporting")
            cd92df73e504 ("ANDROID: power: wakeup: Add last wake up source logging for suspend abort reason.")
            546b6ae3c087 ("ANDROID: power: wakeup: Add the guard condition for len in pm_get_active_wakeup_sources")
            1453d9ffcdbe ("ANDROID: power: wakeup_reason: make logging work in an interrupt context.")]
Change-Id: I81addaf420f1338255c5d0638b0d244a99d777d1
Signed-off-by: Alistair Strachan <astrachan@google.com>