thermal: pm8xxx-tm: Improve temp alarm logging and notification filtering

Modify the kernel log message which is output when the PMIC
temperature alarm triggers so that the current (or estimated)
PMIC die temperature is shown regardless of ADC type.

Also change the log message printing and userspace notification
logic so that they only happen when the PMIC temp alarm stage
differs from what was previously seen.  This will reduce the
number of messages seen while the temperature fluctuates around
one of the thresholds.

Change-Id: I5ee2206ea05dee86666308d11dad1fc5560e58e0
Signed-off-by: David Collins <collinsd@codeaurora.org>