New protocol decoder: hdcp

libsigrokdecode now supports yet another protocol decoder: hdcp.

This one stacks on top of the i2c decoder and decodes the High-bandwidth Digital Content Protection (HDCP) protocol mapped to HDMI.

Some example traces are available in the sigrok-dumps repo and some test-cases in the sigrok-test repo, as usual.

The decoder was contributed by Dave Craig, thanks a lot!