[llvm] [RISCV] Implement RISCVTTIImpl::getPreferredAddressingMode for HasVendorXCVmem (PR #120533)

[Philipp van Kempen via llvm-commits]

PhilippvK wrote:

@ChunyuLiao I think [this patch](https://github.com/openhwgroup/corev-llvm-project/commit/c8580ec9f8928c04eb1ea30ca876c252beefd4b0) was missed when [upstreaming codegen support](https://github.com/llvm/llvm-project/commit/2afea7296812b7e12c6ec683e6858bd4cbe8dd8d) for XCVmem.

https://github.com/llvm/llvm-project/pull/120533