[llvm] [RISCV][EVL] Disable EVLIndVarSimplify Pass by default (PR #151483)

[Shih-Po Hung via llvm-commits]

arcbbb wrote:

Sure, I started by adding an option to disable it by default in #151483, while still allowing it to be re-enabled manually.

https://github.com/llvm/llvm-project/pull/151483