dt-bindings: Add Broadcom AVS RO thermal

Since the BCM2711 doesn't have a AVS TMON block, the thermal information
must be retrieved from the AVS ring oscillator block. This block is part
of the AVS monitor which contains a bunch of raw sensors.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1578941778-23321-2-git-send-email-stefan.wahren@i2se.com