kerne-command-line: introduce option 'systemd.restore_state'

When set to 0 this will stop tools like the backlight and rfkill tools to
restore state from previous boot. This is useful in case the stored state
is bogus to the extent that it is preventing you from resetting it (e.g.,
the backlight settings cause the screen to be off on boot on a system where
the backlight can not be adjusted directly from the keyboard).

src/backlight/backlight.c

@@ -24,6 +24,7 @@
 #include "fileio.h"
 #include "libudev.h"
 #include "udev-util.h"
+#include "util.h"
 
 static struct udev_device *find_pci_or_platform_parent(struct udev_device *device) {
         struct udev_device *parent;
@@ -290,7 +291,7 @@ int main(int argc, char *argv[]) {
          * device probing should be complete), so that the validity
          * check at boot time doesn't have to be reliable. */
 
-        if (streq(argv[1], "load")) {
+        if (streq(argv[1], "load") && restore_state()) {
                 _cleanup_free_ char *value = NULL;
 
                 if (!validate_device(udev, device))