acpi: add implementation of aml_while() term

Commit 68e6b0a (acpi: add aml_while() term) added
the definition of aml_while without the actual implementation.
Implement the term.

Signed-off-by: Marcel Apfelbaum <marcel@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Laszlo Ersek <lersek@redhat.com>

hw/acpi/aml-build.c

@@ -687,6 +687,14 @@ Aml *aml_else(void)
     return var;
 }
 
+/* ACPI 1.0b: 16.2.5.3 Type 1 Opcodes Encoding: DefWhile */
+Aml *aml_while(Aml *predicate)
+{
+    Aml *var = aml_bundle(0xA2 /* WhileOp */, AML_PACKAGE);
+    aml_append(var, predicate);
+    return var;
+}
+
 /* ACPI 1.0b: 16.2.5.2 Named Objects Encoding: DefMethod */
 Aml *aml_method(const char *name, int arg_count)
 {