i965/reg_allocate: Use make_reg_conflicts_transitive

i965/reg_allocate: Use make_reg_conflicts_transitive

Instead of adding transitive conflicts as we go, we now add regular
conflicts and them make them all transitive at the end.  This reduces
screen creation time substantially on BDW.  The time spent in eglInitialize
is reduced from 27.78 ms/call to 9.92 ms/call in debug mode and from 13.15
ms/call to 4.54 ms/call in release mode (about 65% in either case).

Reviewed-by: Eric Anholt <eric@anholt.net>