i965: Implement b2f and b2i using negation.

i965: Implement b2f and b2i using negation.

Booleans are represented as 0/-1 on modern hardware which means we can
just negate them to convert them into a numeric type.  Negation has
the benefit that it can be implemented using a source modifier which
can easily be propagated into some other instruction.  shader-db
results on HSW:

total instructions in shared programs: 6349082 -> 6346693 (-0.04%)
instructions in affected programs:     40948 -> 38559 (-5.83%)
helped:                                123
HURT:                                  1
GAINED:                                1
LOST:                                  0

Reviewed-by: Matt Turner <mattst88@gmail.com>