[AArch64] Add tests for umax(x, 1u)

This patch adds tests for umax(x, 1u).

This patch fixes:

https://github.com/llvm/llvm-project/issues/60233

It turns out that commit 86b4d864 on
Feb 8, 2023 already performs the instcombine transformation proposed
in the issue, so the issue requires no change on the codegen side.