dyndbg: use the module notifier callbacks

Bring dynamic debug in line with other subsystems by using the module
notifier callbacks. This results in a net decrease in core module
code.

Additionally, Jim Cromie has a new dynamic debug classmap feature,
which requires that jump labels be initialized prior to dynamic debug.
Specifically, the new feature toggles a jump label from the existing
dynamic_debug_setup() function. However, this does not currently work
properly, because jump labels are initialized via the
'module_notify_list' notifier chain, which is invoked after the
current call to dynamic_debug_setup(). Thus, this patch ensures that
jump labels are initialized prior to dynamic debug by setting the
dynamic debug notifier priority to 0, while jump labels have the
higher priority of 1.

Tested by Jim using his new test case, and I've verfied the correct
printing via: # modprobe test_dynamic_debug dyndbg.

Link: https://lore.kernel.org/lkml/20230113193016.749791-21-jim.cromie@gmail.com/
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202302190427.9iIK2NfJ-lkp@intel.com/
Tested-by: Jim Cromie <jim.cromie@gmail.com>
Reviewed-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
CC: Jim Cromie <jim.cromie@gmail.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

include/linux/module.h

@@ -27,6 +27,7 @@
 #include <linux/tracepoint-defs.h>
 #include <linux/srcu.h>
 #include <linux/static_call_types.h>
+#include <linux/dynamic_debug.h>
 
 #include <linux/percpu.h>
 #include <asm/module.h>
@@ -579,6 +580,9 @@ struct module {
 	struct error_injection_entry *ei_funcs;
 	unsigned int num_ei_funcs;
 #endif
+#ifdef CONFIG_DYNAMIC_DEBUG_CORE
+	struct _ddebug_info dyndbg_info;
+#endif
 } ____cacheline_aligned __randomize_layout;
 #ifndef MODULE_ARCH_INIT
 #define MODULE_ARCH_INIT {}