AArch64: Add fake arm64 backend, and disable it by method filter.

Just create an ArmCodeGenerator for arm64, but currently no code will
be generated for arm64.

The method filter can:
1. Skip methods with unsupported prototype.
2. Skip methods with unsupported dalvik byte code.
3. Skip methods with invocation to unsupported prototype.

These are temporary codes and should be removed later. But with this
patch, it won't break anything when we merge partly implemented arm64
backend later.

Change-Id: Ib9180d7b8a978f0a5ebaf6b4893e7e3724897113