[clang] [llvm] [RISC-V] Add support for MIPS P8700 CPU (PR #117865)

[Michael Maitland via cfe-commits]

michaelmaitland wrote:

Please split a3ed3550aed41e102bf41ec347f19f9a3c339b2b into multiple commits (and eventually PRs). One for CPU definition and one for scheduler model. 

https://github.com/llvm/llvm-project/pull/117865