implement WSDISPLAYIO_{GET|PUT}CMAP ioctl()s
while there:
- unmap registers and vram only in WSDISPLAYIO_MODE_MAPPED ( so DRM can map
  them ) but not in WSDISPLAYIO_MODE_DUMBFB ( so wsfb can do things that
  require hardware access, like palette and cursor ioctl()s )
- reject ioctl()s that need hardware access if registers are unmapped ( so we
  don't crash instead )
- use the same bit order in cursor sprite images as the other drivers do
with all this, Xorg with wsfb works properly on top of radeonfb

tested on i386 and macppc ( fingers crossed for alpha ;) )

(macallan)