Relocate global sm variable to reduce include file deps

The new state machine handling is not necessary to export to external
plugins, so this patch reduces the exposure of the global variable sm

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

sm.h

@@ -40,6 +40,8 @@ typedef struct sm {
 	int in_teardown;          /* Set when waiting for all processes to be halted */
 } sm_t;
 
+extern sm_t  sm;
+
 void sm_init(sm_t *sm);
 void sm_step(sm_t *sm);
 void sm_set_runlevel(sm_t *sm, int newlevel);