[Clang][RISCV] Bump rvv intrinsics version to v0.12

The LLVM now supports v0.12 of the RVV intrinsics. Users can use the macro
riscv_v_intrinsic to distinguish what kind of intrinsics is supported in
the compiler.

Please refer to tag descriptions under

https://github.com/riscv-non-isa/rvv-intrinsic-doc/tags

Reviewed By: kito-cheng

Differential Revision: https://reviews.llvm.org/D156394