thermal: qcom-spmi-temp-alarm: correct IRQ triggering for GEN2 peripherals

The interrupt signal output by GEN2 TEMP_ALARM peripherals
differs from that of early versions.  Instead of outputting a
short pulse on each over-temperature stage transition, it outputs
low for stage 0 and high for stage > 0.  This means that
interrupt triggering needs to be configured for the falling edge
to receive a notification of the stage 1 to 0 transition.

Modify the qcom-spmi-temp-alarm driver so that it triggers on
both rising and falling edges for TEMP_GEN2 subtype peripherals
and only on the rising edge for older subtypes.

Change-Id: Icc161317a38aa9618c1e20c99473ac7ee803956b
Signed-off-by: David Collins <collinsd@codeaurora.org>