Re-factor the console-related code into fdt_console.[ch]

Instead of requiring drivers to be explicit about their device memory
mapping requirements, move this decision into the fdt layer. This
introduces a new MD function, fdtbus_bus_tag_create, which is responsible
for returning per-node bus_space handles.

Merge thorpej-cfargs2.

branches: 1.8.4;
Specify the "fdt" interface attribute when configuring via FDT, since
mainbus also carries the "mainbus" interface attribute.

branches: 1.7.2; 1.7.4;
Merge thorpej-cfargs branch:

Simplify and make extensible the config_search() / config_found() /
config_attach() interfaces: rather than having different variants for
which arguments you want pass along, just have a single call that
takes a variadic list of tag-value arguments.

Adjust all call sites:
- Simplify wherever possible; don't pass along arguments that aren't
actually needed.
- Don't be explicit about what interface attribute is attaching if
the device only has one. (More simplification.)
- Add a config_probe() function to be used in indirect configuiration
situations, making is visibly easier to see when indirect config is
in play, and allowing for future change in semantics. (As of now,
this is just a wrapper around config_match(), but that is an
implementation detail.)

Remove unnecessary or redundant interface attributes where they're not
needed.

There are currently 5 "cfargs" defined:
- CFARG_SUBMATCH (submatch function for direct config)
- CFARG_SEARCH (search function for indirect config)
- CFARG_IATTR (interface attribte)
- CFARG_LOCATORS (locators array)
- CFARG_DEVHANDLE (devhandle_t - wraps OFW, ACPI, etc. handles)

...and a sentinel value CFARG_EOL.

Add some extra sanity checking to ensure that interface attributes
aren't ambiguous.

Use CFARG_DEVHANDLE in MI FDT, OFW, and ACPI code, and macppc and shark
ports to associate those device handles with device_t instance. This
will trickle trough to more places over time (need back-end for pre-OFW
Sun OBP; any others?).

branches: 1.6.4;
faa_a4x_bst is gone

We don't need to call the POW and FGA bootstrap functions from the FDT
mainbus attach, the iobus attach code does this already and is called
for both iobus-only and FDT cases anyway.

After discussion with jmcneill@.

Attach an iobus with octrnm even if using devicetree (there is no
corresponding node for this device in the DT).

Initialize FDT console device

FDT support for Cavium OCTEON MIPS SoCs. WIP.

branches: 1.1.2; 1.1.18;
Initial import of Cavium Octeon and Octeon Plus SoC and
specifically Ubiquiti Networks EdgeRouter LITE support.
Currently the ethernet and uart are worked.
This support was contributed by Internet Initiative Japan Inc.