thermal: int340x: processor_thermal: Add mailbox driver

thermal: int340x: processor_thermal: Add mailbox driver

Added processor thermal device mail box interface for workload hints
setting. These hints will give indication to hardware to better manage
power and thermals. The supported hints are:
idle
semi_active
burusty
sustained
battery_life

For example when the system is on battery, the hardware can be less
aggressive in power ramp up.

This will create an attribute group at
/sys/bus/pci/devices/0000:00:04.0/workload_request

This folder contains two attributes:
workload_available_types : (RO):  This shows available workload types
workload_type: (RW) : Allows to set and get current workload type
setting

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/20201126171829.945969-4-srinivas.pandruvada@linux.intel.com