Improve detection of addressing mode in e6000sw

Some devices cannot rely on the switch MDIO address passed in the DTB
for specifying single/multi-chip addressing mode. Introduce new property
"single-chip-addressing" which added to DTS will force single-chip mode.

Submitted by: Michal Mazur <mkm@semihalf.com>
Obtained from: Semihalf
Sponsored by: Stormshield
Differential Revision: https://reviews.freebsd.org/D14800

sys/dev/etherswitch/e6000sw/e6000sw.c

@@ -213,7 +213,9 @@ e6000sw_probe(device_t dev)
 	if (OF_getencprop(sc->node, "reg", &sc->sw_addr,
 	    sizeof(sc->sw_addr)) < 0)
 		return (ENXIO);
-	if (sc->sw_addr != 0 && (sc->sw_addr % 2) == 0)
+
+	if (!OF_hasprop(sc->node, "single-chip-addressing") &&
+	    (sc->sw_addr != 0 && (sc->sw_addr % 2) == 0))
 		sc->multi_chip = true;
 
 	/*