i965: Use Ivybridge's "Legacy Data Port" for reads/writes.

i965: Use Ivybridge's "Legacy Data Port" for reads/writes.

Using the constant cache for reads isn't going to work for scratch
reads (variably-indexed arrays or register spills), as these aren't
constant at all.

Also, in the new VS backend, use the proper message number for OWord
Dual Block Write messages.  It's now 10, instead of 9.

+205 piglits.

NOTE: This is a candidate for the 7.11 branch.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>