[LoongArch] Add Scalar link component

Fix the lld link error on ppc64le builders:
```
ld.lld: error: undefined symbol: llvm::createLoopDataPrefetchPass()
>>> referenced by LoongArchTargetMachine.cpp
>>>               lib/Target/LoongArch/CMakeFiles/LLVMLoongArchCodeGen.dir/LoongArchTargetMachine.cpp.o:((anonymous namespace)::LoongArchPassConfig::addIRPasses())
collect2: error: ld returned 1 exit status`
```

Reviewed By: sdesmalen

Differential Revision: https://reviews.llvm.org/D146806