i965: make GT3 machines work as GT3 instead of GT2

i965: make GT3 machines work as GT3 instead of GT2

We were not allowed to say the "GT3" name, but we really needed to
have the PCI IDs because too many people had such machines, so we had
to make the GT3 machines work as GT2.

Let's just say that GT2_PLUS was a short for GT2_PLUS_1 :)

NOTE: This is a candidate for stable branches.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>