qsfp_x32: monitor the main QSFP V3P3 rail

[Aaron-Hartwig]

Right now the enable is just tied on and the pg/alert pins go nowhere (https://github.com/oxidecomputer/quartz/blob/main/hdl/projects/sidecar/qsfp_x32/QsfpX32ControllerTop.bsv#L769-L771).