[llvm] [RISCV]Add support for resolving encoding conflicts among vendor specific CSRs (PR #96174)

[Craig Topper via llvm-commits]

topperc wrote:

Please retitle this patch and update the description. The only thing in this patch is a new tablegen feature that should be described on its own. The RISC-V use case can be used to justify it, but should not be the primary description.

https://github.com/llvm/llvm-project/pull/96174