[llvm] [clang] [RISCV] Add support for Smepmp 1.0 (PR #78489)

[Min-Yih Hsu via cfe-commits]

mshockwave wrote:

> Needs to be added to RISCVUsage.rst, and probably a note in the release docs as well.

It's done now.

https://github.com/llvm/llvm-project/pull/78489