[llvm] [MIPS] Fix the opcode of max.fmt and mina.fmt and make them matchable by ISel (PR #85609)

[YunQiang Su via llvm-commits]

wzssyqa wrote:

The first patch should only fix the encoding problem (including the test cases about it)
The 2nd patch should add the backend support.

https://github.com/llvm/llvm-project/pull/85609