Add a function for adding connections dynamically. This also removes
the 1:1 mapping between port number and the index into the connections
array. The only place this mapping was used was in the warning for
duplicate output ports, which has been replaced by a search. Other
uses of the port number already use the port member variable.

Being able to dynamically add connections will allow other devices like
CTI to re-use the connection mechanism despite not having explicit
connections described in the DT.

The connections array is now no longer sparse, so child_fwnode doesn't
need to be checked as all connections have a target node. Because the
array is no longer sparse, the high in and out port numbers are required
for the refcount arrays. But these will also be removed in a later
commit when the refcount is made a property of the connection.
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: James Clark <james.clark@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230425143542.2305069-7-james.clark@arm.com