Want support for decoding datapath information

[bnaecker]

During bringup of our first customer rack, we looked in detail at an array of transceiver state related to the datapath. It would be helpful to have first-class decoding and xcvradm printing of this information. This includes:

• Tx disable bits
• Tx LOS / LOL
• Rx LOS / LOL
• Tx / Rx CDR enabled
• Tx fault (adaptive EQ and laser)
• Datapath state (for CMIS modules, not directly supported for SFF-8636)

There is a lot of other information we could gather, but which might be less important:

• Max Tx input equalization
• Max Rx output emphasis and emphasis type
• Host / media side FEC support and enabled state
• Tx squelch, adaptive EQ freeze
• Rx squelch
• Rx output disabled (might be in the first list, but never seen this set)
• TC / CTLE stabilization time

[Aaron-Hartwig]

@bnaecker I have everything you noted in your second batch of bullet points as part of my WIP branch, so no need to worry about that on your end. We should sync about how we want to expose all this info as I think we are looking at very adjacent things