To facilitate use by SoC implementors working with bhnd-inheriting fdt/nexus
drivers:
- Splits bhnd_bus method implementations into generic bus implementations (bhnd_bus_generic) and generic bhnd(4) driver implementations (bhnd_generic)
- Simplifies bhnd resource handling, allowing bhnd bus implementations to support bhnd resource activation by implementing the standard BUS_* resource APIs and BHND_BUS_ACTIVATE_RESOURCE().
Depends on D5757