i965: Add support for IF/ELSE/ENDIF control flow on Ivybridge.

i965: Add support for IF/ELSE/ENDIF control flow on Ivybridge.

Ivybridge's IF instruction doesn't support conditional modifiers.
It also introduces UIP, which must point to the ENDIF instruction.

ELSE and ENDIF remain the same except that JIP moves from dst to src1.

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