[RISCV] Pretty print AVL register in VSETVLIInfo::dump. NFC

Currently the AVLReg is printed raw like {AVLReg=2147483668, ...}, this
changes it to {AVLReg=%20, ...} which should be easier to read.

Author: lukel97

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp

@@ -833,7 +833,7 @@ class VSETVLIInfo {
     if (isUnknown())
       OS << "unknown";
     if (hasAVLReg())
-      OS << "AVLReg=" << (unsigned)getAVLReg();
+      OS << "AVLReg=" << llvm::printReg(getAVLReg());
     if (hasAVLImm())
       OS << "AVLImm=" << (unsigned)AVLImm;
     if (hasAVLVLMAX())