omap-common: Common serial and usbethaddr functions based on die id

Now that we have a common prototype to grab the omap die id, functions to figure
out a serial number and usb ethernet address can use it directly.
Those also get an omap_die_id prefix for better consistency.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/board/ti/beagle/beagle.c b/board/ti/beagle/beagle.c
index b0d06a5..149b5db 100644
--- a/board/ti/beagle/beagle.c
+++ b/board/ti/beagle/beagle.c
@@ -506,12 +506,8 @@
 	musb_register(&musb_plat, &musb_board_data, (void *)MUSB_BASE);
 #endif
 
-	if (generate_fake_mac) {
-		unsigned int die_id[4] = { 0 };
-
-		omap_die_id(die_id);
-		usb_fake_mac_from_die_id(die_id);
-	}
+	if (generate_fake_mac)
+		omap_die_id_usbethaddr();
 
 	return 0;
 }