[feature] Add properties to Interface (#3238)

Enable a user to define Scala-time properties on an Interface.  These
properties require a conformance to examine.  This enables patterns where
a client wants to configure itself based on knowledge of the component,
e.g., when the client is a testbench.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>