Merge thorpej-cfargs2.

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 a

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?).

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fix some tpyos, add some comments

use rasops_init(0, 0)

- add support for running the console in 8 bit colour
- make shadow fb optional
- use VCONS_DONT_READ if there's no shadow fb

add the missing bits to allow X to run in 24bit with the wsfb driver
still no hardware acceleration though

use a shadow framebuffer

first stab at a driver for the cg12 / matrox cg3
for now it uses the same monochrome overlay as OBP, otherwise it's got the
usual wsdisplay / vcons goodies
TODO:
- fill in mmap and ioctl methods so w

first stab at a driver for the cg12 / matrox cg3
for now it uses the same monochrome overlay as OBP, otherwise it's got the
usual wsdisplay / vcons goodies
TODO:
- fill in mmap and ioctl methods so we can at least run X in monochrome
- figure out where the 24bit buffer is ( and maybe if there's an 8 bit buffer )
- see if we can do any acceleration
- find the DAC registers

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