Add fan hotswap PG's to sequencer ring buf

[nathanaelhuffman]

We don't allow sequencing from A2 if we don't have PGs from the 3 fan controllers. We don't currently report these pin states in a sequence timeout so we just timeout in IDLE since the FPGA didn't move. We should report more info here.

This plays into #2372 as well

[hawkw]

These should probably also be included in an ereport when we emit one on sequencing timeouts...

[nathanaelhuffman]

Yep definitely, and I think if they're not happy we could just not start sequencing and report that rather than waiting for the timeout since we know that apriori