[ARM64] Add a missed case label for arm64_be, and enable the aarch64-varargs test for arm64_be.

This ensures that r203917 (cpirker "AArch64_be varargs processing for ARM ABI") is ported to ARM64.
[ARM64] Enable the test aarch64-type-sizes.c for ARM64 BE.

This completes the port of r203918 (cpirker "AArch64_be specific clang target settings") to ARM64.
[ARM64] Change inline assembly constraints to be more lax, to match the behaviour of Clang/AArch64 and GCC.

GCC allows sub-64bit values to use the 'r' register constraint.
[ARM64] Enable more CodeGen tests for ARM64. The crypto and neon intrinsics tests needed changing slightly due to the naming differences between AArch64 and ARM64.
[ARM64] Add a big endian version of the ARM64 target machine, and update all users.

This completes the porting of r202024 (cpirker "Add AArch64 big endian Target (aarch64_be)") to ARM64.