thermal/drivers/mediatek/lvts_thermal: Use offset threshold for IRQ

There are two kinds of temperature monitoring interrupts available:
* High Offset, Low Offset
* Hot, Hot to normal, Cold

The code currently uses the hot/h2n/cold interrupts, however in a way
that doesn't work: the cold threshold is left uninitialized, which
prevents the other thresholds from ever triggering, and the h2n
interrupt is used as the lower threshold, which prevents the hot
interrupt from triggering again after the thresholds are updated by the
thermal framework, since a hot interrupt can only trigger again after
the hot to normal interrupt has been triggered.

But better yet than addressing those issues, is to use the high/low
offset interrupts instead. This way only two thresholds need to be
managed, which have a simpler state machine, making them a better match
to the thermal framework's high and low thresholds.

Fixes: f5f633b1 ("thermal/drivers/mediatek: Add the Low Voltage Thermal Sensor driver")
Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230706153823.201943-4-nfraprado@collabora.com