Combine multiple defs of arm64 register sets

Combine multiple defs of arm64 register sets

Summary:
This patch aims to combine similar arm64 register set definitions defined in NativeRegisterContextLinux_arm64 and RegisterContextPOSIX_arm64.
I have implemented a register set interface out of RegisterInfoInterface class and moved arm64 register sets into RegisterInfosPOSIX_arm64 which is similar to Utility/RegisterContextLinux_* implemented by various other targets. This will help in managing register sets of new ARM64 architecture features in one place.

Built and tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabihf targets.

Reviewers: labath

Reviewed By: labath

Subscribers: mhorne, emaste, kristof.beyls, atanasyan, danielkiss, lldb-commits

Differential Revision: https://reviews.llvm.org/D80105