i965: Fix INTDIV math assertions on Broadwell.

i965: Fix INTDIV math assertions on Broadwell.

Commit c66d928f2c9fa59e162c391fbdd37df969959718 ("i965: Enable INTDIV
in SIMD16 mode.") began using generate_math_gen6 to break SIMD16 INTDIV
into two SIMD8 operations.

generate_math_gen6 takes two registers - for unary operations, we pass
ARF null for the second operand.  Prior to Broadwell, real operands were
always GRF.  But now they can be IMM as well.

So, check for != ARF instead of == GRF.

+12 piglits.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>