[RISC-V][ISel] Remove redundant czero.eqz like 'czero.eqz a0, a0, a0' (#90208)

In RISC-V ISel, the instruction `czero.eqz a0, a0, a0` is meaningless.
This patch does the following folds in ISel:
```
czero_eqz x, (setcc x, 0, ne) -> x
czero_nez x, (setcc x, 0, eq) -> x
```

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Signed-off-by: Zhijin Zeng <zhijin.zeng@spacemit.com>