Documentation: bindings: add compatible specific to pre v1.0 SCPI protocols

This patch adds specific compatible to support all the unversioned SCPI
protocols prior to v1.0 release. This will be applicable for all the
implementations using draft versions or modified versions of those
draft vesrions of SCPI protocol.

Cc: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>