amd64: Initialize IPI scoreboard earlier

Scoreboard is needed a moment when smp_started == true.  If some kernel
daemon thread is started before scoreboard is inited, and does some pmap
operation that requires TLB maintanence, which races with SMP startup,
we might dereference NULL invl_scoreboard.  This is particularly easy
to trigger when EARLY_AP_STARTUP is not defined.

Reported by:	glebius
Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Differential revision:	https://reviews.freebsd.org/D36766

sys/amd64/amd64/mp_machdep.c

@@ -579,7 +579,7 @@ invl_scoreboard_init(void *arg __unused)
 		invl_op_pg = INVL_OP_PG;
 	}
 }
-SYSINIT(invl_ops, SI_SUB_SMP, SI_ORDER_FIRST, invl_scoreboard_init, NULL);
+SYSINIT(invl_ops, SI_SUB_SMP - 1, SI_ORDER_ANY, invl_scoreboard_init, NULL);
 
 static uint32_t *
 invl_scoreboard_getcpu(u_int cpu)