i965: Expand uniform args to gen6 math to full registers to get hstride == 1.

i965: Expand uniform args to gen6 math to full registers to get hstride == 1.

This is a hw requirement in math args.  This also is inefficient, as
we're calculating the same result 8 times, but then we've been doing
that on pre-gen6 as well.  If we're doing math on uniforms, though,
we'd probably be better served by having some sort of mechanism for
precalculating those results into another uniform value to use.

Fixes 7 piglit math tests.