util-lib: move /proc/cmdline parsing code to proc-cmdline.[ch]

src/shared/bus-util.c

@@ -47,6 +47,7 @@
 #include "unit-name.h"
 #include "utf8.h"
 #include "util.h"
+#include "proc-cmdline.h"
 
 static int name_owner_change_callback(sd_bus_message *m, void *userdata, sd_bus_error *ret_error) {
         sd_event *e = userdata;

src/shared/condition.c

@@ -39,6 +39,7 @@
 #include "mount-util.h"
 #include "parse-util.h"
 #include "path-util.h"
+#include "proc-cmdline.h"
 #include "selinux-util.h"
 #include "smack-util.h"
 #include "stat-util.h"