Fix compilation of arm's AVILA.

Compilation of the AVILA kernel failed because of two reasons:

- It needed curthread, which is defined through <sys/pcpu.h>.

- It still referred the softc's sc_mtx field, which has been replaced by
  sc_lock three weeks ago.

To solve the first problem, I decided to include <sys/pcpu.h> in
<sys/sx.h>, which also seems to be done by <sys/mutex.h> and
<sys/rwlock.h>. Those header files also require curthread.

Approved by:	jhb

sys/dev/iicbus/ad7418.c

@@ -120,7 +120,7 @@ ad7418_attach(device_t dev)
 	int conf;
 
 	sc->sc_dev = dev;
-	sx_init(&sc->sc_mtx, "ad7418");
+	sx_init(&sc->sc_lock, "ad7418");
 
 	SYSCTL_ADD_PROC(ctx, SYSCTL_CHILDREN(tree), OID_AUTO,
 		"temp", CTLTYPE_INT | CTLFLAG_RD, sc, 0,

sys/sys/sx.h

@@ -34,9 +34,10 @@
 
 #include <sys/_lock.h>
 #include <sys/_sx.h>
-#include <sys/lock_profile.h>
 
 #ifdef	_KERNEL
+#include <sys/pcpu.h>
+#include <sys/lock_profile.h>
 #include <machine/atomic.h>
 #endif