[clang] [llvm] [RISCV] Add Andes A25/AX25 processor definition (PR #140681)

[Min-Yih Hsu via cfe-commits]

================

----------------
mshockwave wrote:

I propose writing `test/Driver/print-enabled-extensions` tests instead for testing extensions.

https://github.com/llvm/llvm-project/pull/140681