dt-bindings: arm,vexpress-juno: Add missing motherboard properties

The arm,vexpress-juno binding is missing 'ranges', 'arm,vexpress,site', and
'arm,hbi' properties. Add these and and restrict additional properties to
be nodes only.

Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210819184239.1192395-3-robh@kernel.org