AArch64: fixes in A64 code generation.

- Disabled special method compilation, as it requires hard-float ABI,
- Disabled suspend checks, as runtime is not yet ready (e.g. trampolines
  are not setting the suspend register, etc),
- Changing definition of zero register (the zero register has now 0x3f
  as its register number),
- Fixing some issues with handling of cmp instructions in the assembler:
  we now use the shift-register rather than the extended-register variant
  of cmp and cmn,
- Partially fixing register setup (register sN is now mapped to dN),
- Fixing and completing implementation of register spills/unspills,
- Fixing LoadBaseDispBody() and StoreBaseDispBody().

Change-Id: Ia49ba48b6ca0f782380066345b7a198cb6c1dc1d