Cranelift: Add instructions for getting the current stack/frame/return pointers (#4573)

* Cranelift: Add instructions for getting the current stack/frame pointers and return address

This is the initial part of https://github.com/bytecodealliance/wasmtime/issues/4535

* x64: Remove `Amode::RbpOffset` and use `Amode::ImmReg` instead

We just special case getting operands from `Amode`s now.

* Fix s390x `get_return_address`; require `preserve_frame_pointers=true`

* Assert that `Amode::ImmRegRegShift` doesn't use rbp/rsp

* Handle non-allocatable registers in Amode::with_allocs

* Use "stack" instead of "r15" on s390x

* r14 is an allocatable register on s390x, so it shouldn't be used with `MovPReg`

cranelift/interpreter/src/step.rs

@@ -1032,6 +1032,9 @@ where
         Opcode::ExtractVector => {
             unimplemented!("ExtractVector not supported");
         }
+        Opcode::GetFramePointer => unimplemented!("GetFramePointer"),
+        Opcode::GetStackPointer => unimplemented!("GetStackPointer"),
+        Opcode::GetReturnAddress => unimplemented!("GetReturnAddress"),
     })
 }