[LLDB] Fix Cpsr size for WoA64 target

CPSR on Arm64 is 4 bytes in size but windows on Arm implementation is trying to read/write 8 bytes against a byte register causing LLDB unit tests failures.

Ref: https://docs.microsoft.com/en-us/windows/win32/api/winnt/ns-winnt-arm64_nt_context

Reviewed By: mstorsjo

Differential Revision: https://reviews.llvm.org/D112471