[GlobalISel][Mips] Global ISel for `brcond`

- Enable equivalent between `brcond` and `G_BRCOND`.
- Remove the manual selection of `G_BRCOND` in Mips. Revise test cases.

Reviewers: petar-avramovic, bcardosolopes, arsenm

Reviewed By: arsenm

Pull Request: https://github.com/llvm/llvm-project/pull/81306