[RISCV] Add Zfh RUN lines to calling-conv-half.ll. NFC (#156562)
We had these RUN lines in our downstream and I couldn't tell for sure
that we had another Zfh calling convention test upstream.
Note we should fix the stack test to also exhaust the GPRs to make it
test the stack for ilp32f/lp64f. This was an existing issue in the
testing when F was enabled.