Need means of getting persistent versus current active slots

[rmustacc]

The host phase 1 image has a notion of which slot should be selected on cold power up which is stored in a sector of the host SPI flash rom. The faux-mags ComponentSetActiveSlot allows this to be changed persistently or transiently. However, the ComponentGetActiveSlot does not have the ability to select between the persistent and non-persistent option. Current implementations of the host logic only return the current in-memory active slot which may have diverged from the persistent one. It's not clear to me what the cleanest way to get at this is while honoring the MGS compatibility needs.