util-lib: move shall_restore_state() to shared/reboot-util

It's just a small function, but it is higher-level functionality.
I don't see a good place for it, reboot-util.[ch] seems least bad

src/shared/reboot-util.c

@@ -6,6 +6,7 @@
 #include "alloc-util.h"
 #include "fileio.h"
 #include "log.h"
+#include "proc-cmdline.h"
 #include "raw-reboot.h"
 #include "reboot-util.h"
 #include "string-util.h"
@@ -96,3 +97,14 @@ int reboot_with_parameter(RebootFlags flags) {
 
         return log_full_errno(flags & REBOOT_LOG ? LOG_ERR : LOG_DEBUG, errno, "Failed to reboot: %m");
 }
+
+int shall_restore_state(void) {
+        bool ret;
+        int r;
+
+        r = proc_cmdline_get_bool("systemd.restore_state", &ret);
+        if (r < 0)
+                return r;
+
+        return r > 0 ? ret : true;
+}

src/shared/reboot-util.h

@@ -11,3 +11,5 @@ typedef enum RebootFlags {
 
 int read_reboot_parameter(char **parameter);
 int reboot_with_parameter(RebootFlags flags);
+
+int shall_restore_state(void);