Fix LLDB elf core dump register access for ARM/AArch64

Summary:
This patch adds support to access AArch64 FP SIMD core dump registers and adds a test case to verify registers.

This patches fixes a bug where doing "register read --all" causes lldb to crash.

Reviewers: labath

Reviewed By: labath

Subscribers: kristof.beyls, danielkiss, lldb-commits

Differential Revision: https://reviews.llvm.org/D77793