Add fflags test that flags are sticky

[davidharrishmc]

For each of the cp_csr_ffflags coverpoints, add a point about staying 1 as well as the coverpoint about going from 0 to 1.

[davidharrishmc]

Tests added, but aren't hit yet, and nonstick versions don't work now either for fsqrt and some converts and frounds. Lockstep simulation seems to show the flags being set, so it's not immediately obvious why the coverage is missing.