[LoongArch] Generate PCALAU12I + JIRL instruction pair for medium codemodel

In LoongArch, when `CodeModel=Medium`, it just increases the jumping
ability of function calls relative to PC, from 2^28 to 2^32.

Depends on D137393

Reviewed By: SixWeining

Differential Revision: https://reviews.llvm.org/D137394