Clean up LT and LG chip descriptions.

"Mach64 LG" is called 3D Rage LT in the specs and ATI press releases.

"Mach64 LT" is unclear.  XFree86 driver doesn't know this chip at all.
Windows display.inf calls it just "mach64 LT" and it uses the same driver as
VT-A/GT-A and older chips.  VT-B/GT-B and better use another driver and all of
those chips have a more descriptive name in the display.inf file.  That makes
me think this chip is not a 3D Rage chip.
Signed-off-by: Ville Syrjälä <syrjala@sci.fi>
Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>