wsdisplay framebuffer info

[Michael <macallan%netbsd.org@localhost>]

Hello,

I'd like to add an ioctl() to wsdisplay which replaces
WSDISPLAYIO_GTYPE, WSDISPLAYIO_GINFO and WSDISPLAYIO_LINEBYTES by
returning a struct that gives a more complete and useful description of
the mappable framebuffer.  
See attached patch for a preliminary proposal.

Pixel size and encoding are combined into a single value which can be
either split up or used in switch() statements - the latter is probably
going to be much more common.

This would take care of the following problems:
- the present ioctl()s don't tell us enough to actually draw into a
  framebuffer - for example there is nothing about actual colour encoding
- because of this the xf86-video-wsfb driver ( and any other userland
  tool that tries to draw into a framebuffer without actual hardware
  knowledge ) can't really be all that generic - currently it has a pile
  of code that tries to guess the pixel encoding from whatever
  WSDISPLAYIO_GTYPE returns which doesn't help at all with new,
  previously unsupported hardware.

The fbi_flags member is unused for now, it could encode things like
acceleration support ( using a yet to be defined interface ), hardware
cursor, overlays etc.

Anything I missed? Comments?

have fun
Michael