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/codegen/src/isa/x64/lower.rs

@@ -914,7 +914,10 @@ fn lower_insn_to_regs<C: LowerCtx<I = Inst>>(
         | Opcode::Call
         | Opcode::CallIndirect
         | Opcode::Trapif
-        | Opcode::Trapff => {
+        | Opcode::Trapff
+        | Opcode::GetFramePointer
+        | Opcode::GetStackPointer
+        | Opcode::GetReturnAddress => {
             implemented_in_isle(ctx);
         }