[RISCV] Add C intrinsics for scalar bitmanip and crypto

This adds riscv_bitmanip and riscv_crypto.h

This is based on the proposed spec here https://github.com/riscv-non-isa/riscv-c-api-doc/pull/44

Tests that previously used builtins directly now use the intrinsics.

Reviewed By: wangpc

Differential Revision: https://reviews.llvm.org/D155647