thermal/core: Rename 'trips' to 'num_trips'

In order to use thermal trips defined in the thermal structure, rename
the 'trips' field to 'num_trips' to have the 'trips' field containing the
thermal trip points.

Cc: Alexandre Bailon <abailon@baylibre.com>
Cc: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linexp.org>
Link: https://lore.kernel.org/r/20220722200007.1839356-8-daniel.lezcano@linexp.org
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>