kernel: rename struct _k_object

Private type, internal to the kernel, not directly associated
with any k_object_* APIs. Is the return value of z_object_find().
Rename to struct z_object.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
diff --git a/scripts/gen_kobject_list.py b/scripts/gen_kobject_list.py
index 943e684..ce644e4 100755
--- a/scripts/gen_kobject_list.py
+++ b/scripts/gen_kobject_list.py
@@ -111,7 +111,7 @@
 #include <syscall_handler.h>
 #include <string.h>
 %}
-struct _k_object;
+struct z_object;
 """
 
 # Different versions of gperf have different prototypes for the lookup
@@ -119,7 +119,7 @@
 # turned into a string, we told gperf to expect binary strings that are not
 # NULL-terminated.
 footer = """%%
-struct _k_object *z_object_gperf_find(void *obj)
+struct z_object *z_object_gperf_find(void *obj)
 {
     return z_object_lookup((const char *)obj, sizeof(void *));
 }
@@ -136,7 +136,7 @@
 }
 
 #ifndef CONFIG_DYNAMIC_OBJECTS
-struct _k_object *z_object_find(void *obj)
+struct z_object *z_object_find(void *obj)
 	ALIAS_OF(z_object_gperf_find);
 
 void z_object_wordlist_foreach(_wordlist_cb_func_t func, void *context)