thermal: pm8xxx-tm: Modify userspace notification method

Change the userspace notification mechanism in the over
temperature interrupt handler from kobject_uevent() to
sysfs_notify() in order to simplify userspace notification
handling.  Ensure that the new notification mechanism is
independent from the current pm8xxx-tm mode.  This means that the
"mode" thermalfs file does not need to be modified in order for
sysfs_notify() to get called in the interrupt handler.

As before, writing "enabled" to mode will enable the software
override of the automatic PMIC hardware stage 2 partial shutdown
and stage 3 full shutdown.  Turning off these features is
typically undesirable and should be avoided unless userspace is
able to take immediate corrective action.

Change-Id: Ibd92b790778fd559df5ce74231e6cf71bef16370
Signed-off-by: David Collins <collinsd@codeaurora.org>