vc4: Improve the accuracy of SIN and COS.

vc4: Improve the accuracy of SIN and COS.

This gets them to pass glsl-sin/cos.  There was an obvious problem that I
was using the FRC code on the scaled input value, which means that we had
a range in [0, 1], while our taylor is most accurate across [-0.5, 0.5].
We can just slide things over, but that means flipping the sign of the
coefficients.  After that, it was just a matter of stuffing more
coefficients in.