[ARM,CDE] Implement GPR CDE intrinsics

Summary:
This change implements ACLE CDE intrinsics that translate to
instructions working with general-purpose registers.

The specification is available at
https://static.docs.arm.com/101028/0010/ACLE_2019Q4_release-0010.pdf

Each ACLE intrinsic gets a corresponding LLVM IR intrinsic (because
they have distinct function prototypes). Dual-register operands are
represented as pairs of i32 values. Because of this the instruction
selection for these intrinsics cannot be represented as TableGen
patterns and requires custom C++ code.

Reviewers: simon_tatham, MarkMurrayARM, dmgreen, ostannard

Reviewed By: MarkMurrayARM

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

Tags: #clang

Differential Revision: https://reviews.llvm.org/D76296