[LoongArch] Support InlineAsm for LSX and LASX

The author of the following files is licongtian <licongtian@loongson.cn>:
- clang/lib/Basic/Targets/LoongArch.cpp
- llvm/lib/Target/LoongArch/LoongArchAsmPrinter.cpp
- llvm/lib/Target/LoongArch/LoongArchISelLowering.cpp

The files mentioned above implement InlineAsm for LSX and LASX as follows:
- Enable clang parsing LSX/LASX register name, such as $vr0.
- Support the case which operand type is 128bit or 256bit when the
  constraints is 'f'.
- Support the way of specifying LSX/LASX register by using constraint,
  such as "={$xr0}".
- Support the operand modifiers 'u' and 'w'.
- Support and legalize the data types and register classes involved in
  LSX/LASX in the lowering process.

Reviewed By: xen0n, SixWeining

Differential Revision: https://reviews.llvm.org/D154931