i965/eu: Set src0 file to IMM on Gen8+ flow control instructions.

i965/eu: Set src0 file to IMM on Gen8+ flow control instructions.

According to the documentation, we need to set the source 0 register
type to IMM for flow control instructinos that have both JIP and UIP.
Out of paranoia, just make all flow control instructions use IMM;
there's no benefit to using ARF anyway, and it could trouble that's
difficult to diagnose.

See commit 9584959123b0453cf5313722357e3abb9f736aa7, which did the
analogous change in the gen8_generator code.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Reviewed-by: Matt Turner <mattst88@gmail.com>