[llvm] [RISCV] Qualify all XCV predicates with !is64Bit. (PR #101074)

[Craig Topper via llvm-commits]

topperc wrote:

> LTGM but I don't know if these extensions will be supported in 64 bits core like https://github.com/openhwgroup/cvw.

Hopefully someone working on XCV can help. CC @realqhc @melonedo @PaoloS02 

https://github.com/llvm/llvm-project/pull/101074