[Analysis][LoongArch] Add sign extension for i32 parameters and returns

In LoongArch ABI spec, we can see that in the LP64D ABI, unsigned 32-bit
types, such as unsigned int, are stored in general-purpose registers as
proper sign extensions of their 32-bit values.

Reference:
https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html#_abi_lp64d

Reviewed By: SixWeining, xen0n

Differential Revision: https://reviews.llvm.org/D151794

(cherry picked from commit fe6716a4)