MAX5970 alerts are ignored

The MAX5970 hotplug controllers in Gimlet have their ALERT_L and I2C lines routed to the SP, but the SP doesn't do anything with the ALERT_L signal nor does it currently act on any of the status registers other than Register::adc_chx_{cs,mon}_XX which implement the ability to obtain the present readings of voltage and current sensors. Information that may be useful to acquire on an alert interrupt includes the contents of the status0, status3 and fault[2:0] registers and the historical peak detectors {max,min}_chx_{cs,mon}_{lsb,msb}, in addition to the circular buffer contents covered by #1545. This could modeled as additional sensors, gathered continuously, and made available upstack in the same manner as the near-real-time samples, but the intent of this ticket is to cover one-shot collection of this data in response to and shortly after an alert.

Start by tracing the Gimlet service-provider handling for the MAX5970 ALERT_L signal and the existing near-real-time sensor path. Review the status0, status3, fault[2:0], historical peak-detector registers, and the circular-buffer context in #1545. Done means an alert triggers one-shot collection shortly afterward and makes the captured data available upstack.