dt-bindings: thermal: Convert Broadcom TMON to YAML

Convert the Broadcom AVS TMON Device Tree binding to YAML to help with
validation.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20211208003727.3596577-12-f.fainelli@gmail.com
Signed-off-by: Rob Herring <robh@kernel.org>