net: dsa: mv88e6xxx: Add mv88e6390 statistics unit init

The statistics unit on the mv88e6390 needs the histogram mode to be
configured in a different register compared to other devices. Add an
ops to do this.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
v2:
  Rename to mv88e6390_g1_stats_set_histogram
  Move into global1.c
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/dsa/mv88e6xxx/mv88e6xxx.h b/drivers/net/dsa/mv88e6xxx/mv88e6xxx.h
index a647e03..d947a0c 100644
--- a/drivers/net/dsa/mv88e6xxx/mv88e6xxx.h
+++ b/drivers/net/dsa/mv88e6xxx/mv88e6xxx.h
@@ -801,6 +801,11 @@ struct mv88e6xxx_ops {
 	 * be read back a leisure but still with a consistent view.
 	 */
 	int (*stats_snapshot)(struct mv88e6xxx_chip *chip, int port);
+
+	/* Set the histogram mode for statistics, when the control registers
+	 * are separated out of the STATS_OP register.
+	 */
+	int (*stats_set_histogram)(struct mv88e6xxx_chip *chip);
 };
 
 enum stat_type {