loading PH4-mini firmware

The PH4-mini firmware (Pixhawk4-mini) is not loaded properly with MP. The problem is that the PH4-mini and the Pixhawk4 both have the same fmuv5 bootloader, so there is no way for the GCS to distinguish the two. We need to use a separate firmware for the two of them, as PH4-mini has no IOMCU.
Ideally we need to display a list of matching firmwares when this happens, and let the user choose.
Right now what happens is that the Pixhawk4 firmware gets loaded, and when it boots it gets stuck with an error trying to update the IOMCU firmware.

No files, tests, or entry points are named. Start by tracing Mission Planner's firmware matching and loading flow for the shared fmuv5 bootloader, then verify the PH4-mini and Pixhawk4 paths. Done means the matching firmware choices can be distinguished and the PH4-mini path no longer attempts an IOMCU update.

Written by the indexing model from the issue text.