thermal/drivers/int340x: processor_thermal: Export mailbox interface

Export the mailbox interface to be used by other modules. Also change
command id and response from u8 to u32 data type.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210517061441.1921901-2-srinivas.pandruvada@linux.intel.com