thermal: add brcmstb AVS TMON driver

The AVS TMON core provides temperature readings, a pair of configurable
high- and low-temperature threshold interrupts, and an emergency
over-temperature chip reset. The driver utilizes the first two to
provide temperature readings and high-temperature notifications to
applications. The over-temperature reset is not exposed to
applications; this reset threshold is critical to the system and should
be set with care within the bootloader.

Applications may choose to utilize the notification mechanism, the
temperature reading mechanism (e.g., through polling), or both.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Doug Berger <opendmb@gmail.com>
Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>