amd64: more immediate kind asserts, remove entity after frame offset is decided

ir/be/amd64/amd64_emitter.c

@@ -260,6 +260,7 @@ static void amd64_emit_addr(const ir_node *const node,
 {
 	ir_entity *entity = addr->immediate.entity;
 	if (entity != NULL) {
+		assert(addr->immediate.kind != X86_IMM_VALUE);
 		if (is_fp_relative(entity)) {
 			entity = NULL; /* only emit offset for frame entities */
 		} else {
@@ -275,6 +276,7 @@ static void amd64_emit_addr(const ir_node *const node,
 		if (entity != NULL) {
 			be_emit_irprintf("%+" PRId32, offset);
 		} else {
+			assert(addr->immediate.kind == X86_IMM_VALUE);
 			be_emit_irprintf("%" PRId32, offset);
 		}
 	}

ir/be/amd64/bearch_amd64.c

@@ -92,6 +92,8 @@ static void amd64_set_frame_offset(ir_node *node, int offset)
 		if (layout->sp_relative)
 			attr->addr.immediate.offset -= get_insn_mode_bytes(attr->insn_mode);
 	}
+	attr->addr.immediate.kind = X86_IMM_VALUE;
+	attr->addr.immediate.entity = NULL;
 }
 
 static int amd64_get_sp_bias(const ir_node *node)