[AMDGPU][GFX11] Add more test coverage for FMA instructions. (#65935)

This is another attempt to update the tests to run for GFX11. Previously
done in <https://reviews.llvm.org/D153269>, and then reverted in
<https://reviews.llvm.org/rG2d3e6c440244ad94777aa13566b0376eb3c088f1>
due to a failure on a buildbot with expensive checks enabled. Commit
4b1702e8 fixed the problem.