Add accurate implementations of frsqrte and fres

The previous code would just translate frsqrte and fres into 1/sqrt(x) and 1/x respectively; that's conceptually correct, but games depend on the implementation details, so make sure we match the hardware.

JMC47 has already done some testing, and the patch appears to works quite well; it fixes a bunch of physics and graphics glitches.  See Issue 7304.

I'll work on cleaning up and submitting a patch to hwtests to verify the behavior of these instructions.