Vector fptosi_sat and fptoui_sat were being expanded by unrolling the vector operation. This doesn't work for scalable vector, so this patch adds a call to TLI.expandFP_TO_INT_SAT if the vector is scalable.
Scalable tests are added for AArch64 and RISCV. Some of the AArch64 fptoi_sat operations should be legal, but that will be handled in another patch.