Changes from upstream to improve compilation when INET or INET6
or none of them is defined.

MFC after: 3 days
Arrange for uart_cpu_fdt's probe() routine to use the same table of compat
strings as uart_bus_fdt's probe().

The bus code uses ofw_bus_search_compatible() and that's not an option in
cpu (console) code -- it runs way before the ofw routines are usable.  So
the console probe has its own loop to search the table, but now at least
there's only one table to be maintained when new devices are added.