coresight: Store in-connections as well as out-connections

This will allow CATU to get its associated ETR in a generic way where
currently the enable path has some hard coded searches which avoid
the need to store input connections.

This also means that the full search for connected devices on removal
can be replaced with a loop through only the input and output devices.

Signed-off-by: James Clark <james.clark@arm.com>