[LLDB] Add ptrace register access for AArch64 SVE registers

This patch adds NativeRegisterContext_arm64 ptrace routines to access
AArch64 SVE register set. This patch also adds a test-case to test
AArch64 SVE register access and dynamic size configuration capability.

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D79699