[lldb][ARM] Add tests for vpush/vpop D registers

Previously we just checked via S regs and were not checking
memory content after pushes.

The vpush test confirms that the fix in https://reviews.llvm.org/D130307
is working.

Memory will only be checked if an "after" state is provided.

Reviewed By: clayborg

Differential Revision: https://reviews.llvm.org/D130468