gdb/python: New method to access list of register groups

Add a new method gdb.Architecture.register_groups which returns a new
object of type gdb.RegisterGroupsIterator.  This new iterator then
returns objects of type gdb.RegisterGroup.

Each gdb.RegisterGroup object just wraps a single reggroup pointer,
and (currently) has just one read-only property 'name' that is a
string, the name of the register group.

As with the previous commit (adding gdb.RegisterDescriptor) I made
gdb.RegisterGroup an object rather than just a string in case we want
to add additional properties in the future.

gdb/ChangeLog:

	* NEWS: Mention additions to Python API.
	* python/py-arch.c (archpy_register_groups): New function.
	(arch_object_methods): Add 'register_groups' method.
	* python/py-registers.c (reggroup_iterator_object): New struct.
	(reggroup_object): New struct.
	(gdbpy_new_reggroup): New function.
	(gdbpy_reggroup_to_string): New function.
	(gdbpy_reggroup_name): New function.
	(gdbpy_reggroup_iter): New function.
	(gdbpy_reggroup_iter_next): New function.
	(gdbpy_new_reggroup_iterator): New function
	(gdbpy_initialize_registers): Register new types.
	(reggroup_iterator_object_type): Define new Python type.
	(gdbpy_reggroup_getset): New static global.
	(reggroup_object_type): Define new Python type.
	* python/python-internal.h

gdb/testsuite/ChangeLog:

	* gdb.python/py-arch-reg-groups.exp: New file.

gdb/doc/ChangeLog:

	* gdb.texi (Registers): Add @anchor for 'info registers
	<reggroup>' command.
	* python.texi (Architectures In Python): Document new
	register_groups method.
	(Registers In Python): Document two new object types related to
	register groups.

gdb/python/py-arch.c

@@ -248,6 +248,20 @@ archpy_registers (PyObject *self, PyObject *args, PyObject *kw)
   return gdbpy_new_register_descriptor_iterator (gdbarch, group_name);
 }
 
+/* Implementation of gdb.Architecture.register_groups (self) -> Iterator.
+   Returns an iterator that will give up all valid register groups in the
+   architecture SELF.  */
+
+static PyObject *
+archpy_register_groups (PyObject *self, PyObject *args)
+{
+  struct gdbarch *gdbarch = NULL;
+
+  /* Extract the gdbarch from the self object.  */
+  ARCHPY_REQUIRE_VALID (self, gdbarch);
+  return gdbpy_new_reggroup_iterator (gdbarch);
+}
+
 /* Initializes the Architecture class in the gdb module.  */
 
 int
@@ -276,6 +290,10 @@ END_PC." },
     "registers ([ group-name ]) -> Iterator.\n\
 Return an iterator of register descriptors for the registers in register\n\
 group GROUP-NAME." },
+  { "register_groups", archpy_register_groups,
+    METH_NOARGS,
+    "register_groups () -> Iterator.\n\
+Return an iterator over all of the register groups in this architecture." },
   {NULL}  /* Sentinel */
 };