rpi: Add identifier for the new CM4

rpi: Add identifier for the new CM4

The Raspberry Pi Foundation released the new Compute Module 4 which we
want to detect, so we can enable Ethernet on it and know the correct
device tree file name.

Note that this sets the Ethernet option to true since the official CM4
IO board has an Ethernet port. But that might not be the case when using
custom ones.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Reviewed-by: Peter Robinson <pbrobinson@gmail.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Matthias Brugger <mbrugger@suse.com>