[llvm] [RISCV] Adopt SpacemitX60's scheduling model for `-mtune=generic` (PR #167008)

[Luke Lau via llvm-commits]

lukel97 wrote:

Here are the benchmark results for `-march=rva22u64_v -O3 -flto` running on a 16GB Banana Pi F3: https://lnt.lukelau.me/db_default/v4/nts/1300?compare_to=1299

508.namd_r is 15% faster, and 520.omnetpp_r, 502.gcc_r and 519.lbm_r are ~8% faster each.

https://github.com/llvm/llvm-project/pull/167008