Make ofwbus as a subclass of simplebus. Remove bogus checking for busy resource.
Remove now duplicated code from ofwbus.c. Move all useful methods into simplebus.c.
Move resource managers for IRQ and memory from ofwbus to nexus.
Other code uses 0 for invalid phandle, so use it in simplebus_get_devinfo() too.
Use linker set for UARTs definition
Move UATRs FDT declarations into appropriate files. Make uart_class structure static where is possible.