lava: Add a device-arm64-bcm2711-rpi-4-b device

This device entry will be used to run tests on the devices with the bcm2711-rpi-4-b device_type.

It uses the release v2021.0 instead of v2019.1 to deploy via NFS because raspberry pi 4 was not supported in that version.

Signed-off-by: Detlev Casanova detlev.casanova@collabora.com