thermal: ACPI: Move the ACPI thermal library to drivers/acpi/

The ACPI thermal library contains functions that can be used to
retrieve trip point temperature values through the platform firmware
for various types of trip points.  Each of these functions basically
evaluates a specific ACPI object, checks if the value produced by it
is reasonable and returns it (or THERMAL_TEMP_INVALID if anything
fails).

It made sense to hold it in drivers/thermal/ so long as it was only used
by the code in that directory, but since it is also going to be used by
the ACPI thermal driver located in drivers/acpi/, move it to the latter
in order to keep the code related to evaluating ACPI objects defined in
the specification proper together.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>