[llvm] [RISCV] Use two ADDIs to do some stack pointer adjustments for special case (PR #94182)

[Liao Chunyu via llvm-commits]

ChunyuLiao wrote:

> Your code appears to be missing the alignment check of the referenced revision. I'd recommend factoring out that code into a helper, and reusing it here if desired.
> 
> You should also be able to do this solely by adjusting Offset and the Lo12 value. adjustReg already knows how to perform the 2 x ADDI trick, so the fact you need this change at all hints of a bug.

Reused adjustReg. Thanks.

https://github.com/llvm/llvm-project/pull/94182