[llvm] [loongarch][DAG][FREEZE] Fix crash when FREEZE a half(f16) type on loongarch (PR #107791)

[YANG Xudong via llvm-commits]

yxd-ym wrote:

> Thanks. Perhaps we should override this interface.
> 
> ```
> bool softPromoteHalfType() const override { return true; }
> ```
> 
> We currently do not have any parameter passing specifications for f16 types，this may also cause the generated code to not meet expectations.

@wangleiat Changed the fix according to your suggestion and updated the tests. Would you please check it?

https://github.com/llvm/llvm-project/pull/107791