[ARM,CDE] Implement CDE S and D-register intrinsics

Summary:
This patch implements the following ACLE intrinsics:

  uint32_t __arm_vcx1_u32(int coproc, uint32_t imm);
  uint32_t __arm_vcx1a_u32(int coproc, uint32_t acc, uint32_t imm);
  uint32_t __arm_vcx2_u32(int coproc, uint32_t n, uint32_t imm);
  uint32_t __arm_vcx2a_u32(int coproc, uint32_t acc, uint32_t n, uint32_t imm);
  uint32_t __arm_vcx3_u32(int coproc, uint32_t n, uint32_t m, uint32_t imm);
  uint32_t __arm_vcx3a_u32(int coproc, uint32_t acc, uint32_t n, uint32_t m, uint32_t imm);

  uint64_t __arm_vcx1d_u64(int coproc, uint32_t imm);
  uint64_t __arm_vcx1da_u64(int coproc, uint64_t acc, uint32_t imm);
  uint64_t __arm_vcx2d_u64(int coproc, uint64_t m, uint32_t imm);
  uint64_t __arm_vcx2da_u64(int coproc, uint64_t acc, uint64_t m, uint32_t imm);
  uint64_t __arm_vcx3d_u64(int coproc, uint64_t n, uint64_t m, uint32_t imm);
  uint64_t __arm_vcx3da_u64(int coproc, uint64_t acc, uint64_t n, uint64_t m, uint32_t imm);

Since the semantics of CDE instructions is opaque to the compiler, the
ACLE intrinsics require dedicated LLVM IR intrinsics. The 64-bit and
32-bit variants share the same IR intrinsic.

Reviewers: simon_tatham, MarkMurrayARM, ostannard, dmgreen

Reviewed By: MarkMurrayARM

Subscribers: kristof.beyls, hiraditya, danielkiss, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D76298