[LoongArch] Emit function call code sequence as `PCADDU18I+JIRL` in medium code model

According to the description of the psABI v2.20:
https://github.com/loongson/la-abi-specs/releases/tag/v2.20, adjustments
are made to the function call instructions under the medium code model.

At the same time, AsmParser has already supported parsing the call36 and
tail36 macro instructions.