sim: Remove SimObject dependency from serialize.hh

Previously Serializable::serializeAll called SimObject::
serializeAll. This created an unnecessary dependency. This
change makes Serializable responsible for the generation
of the checkpoint file, and then the SimObjects will
perform the serialization of the object using that file.

With this change serialize.hh contains only functions
related to the (un)serialization of basic types or
objects that inherit from Serializable. As a general
rule, functions related to the (un)serialization of
specific/other types must be defined in the file that
introduces that type.

Change-Id: I9438b799d7e9d4c992a62c7f9d1f15f3f3250a5a
Signed-off-by: Daniel R. Carvalho <odanrc@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/38740
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>

src/python/pybind11/core.cc

@@ -307,7 +307,7 @@ pybind_init_core(py::module_ &m_native)
      * Serialization helpers
      */
     m_core
-        .def("serializeAll", &Serializable::serializeAll)
+        .def("serializeAll", &SimObject::serializeAll)
         .def("getCheckpoint", [](const std::string &cpt_dir) {
             SimObject::setSimObjectResolver(&pybindSimObjectResolver);
             return new CheckpointIn(cpt_dir);