This is the final bit of work to relax the register allocation
requirements when code generating normal LLVM IR, which rarely
care about the result of inactive lanes. By using _PRED nodes
we can make better use of SVE's reversed instructions.
Also removes a redundant parameter from the min/max tests.
You don't need to change it here, but should we be lowering aarch64_sve_ptrue to AArch64ISD::PTRUE, instead of supporting both forms through isel?