ARM: dts: bcm2711: Enable thermal

This enables thermal for the BCM2711 (used on Raspberry Pi 4) by adding
the AVS monitor and a subnode for the thermal part.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/1578941778-23321-4-git-send-email-stefan.wahren@i2se.com