Clean up VT and GT chip descriptions.

All B revision VT chips are called 264VT3. Verified from pictures of the
chips as the specs are a bit unlear in this.

GT revision B1 is Rage II, B2 is Rage II+. Specs and chip pictures seem
to agree.

VT revision A4 is 264VT2. Revision A3 is probably a plain 264VT.
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>