dt-bindings: firmware: arm,scmi: Restrict protocol child node properties

dt-bindings: firmware: arm,scmi: Restrict protocol child node properties

The SCMI protocol child nodes are missing any constraints on unknown
properties. Specifically, either 'unevaluatedProperties' or
'additionalProperties' is needed. The current structure with a regex
match for all child nodes doesn't work for this purpose, so let's move
the common properties '$defs' entry which each specific protocol node
can reference and set 'unevaluatedProperties: false'.

Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20230124222023.316089-1-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>