[clang] [llvm] [RISCV] Add Qualcomm uC Xqcisls (Scaled Load Store) extension (PR #117987)

[Sam Elliott via cfe-commits]

https://github.com/lenary commented:

The encodings and functionality here are correct, but we're missing a test and it would be good to add a comment to the scaled store tablegen class.

https://github.com/llvm/llvm-project/pull/117987