net: dsa: add new DSA switch driver for the SMSC-LAN9303

The SMSC/Microchip LAN9303 is an ethernet switch device with one CPU port
and two external ethernet ports with built-in phys.

This driver uses the DSA framework, but is currently only capable of
separating the two external ports. There is no offload support yet.
Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/lan9303.h

+#include <linux/regmap.h>
+#include <linux/device.h>
+#include <net/dsa.h>
+
+struct lan9303 {
+	struct device *dev;
+	struct regmap *regmap;
+	struct regmap_irq_chip_data *irq_data;
+	struct gpio_desc *reset_gpio;
+	u32 reset_duration; /* in [ms] */
+	bool phy_addr_sel_strap;
+	struct dsa_switch *ds;
+	struct mutex indirect_mutex; /* protect indexed register access */
+};
+
+extern const struct regmap_access_table lan9303_register_set;
+
+int lan9303_probe(struct lan9303 *chip, struct device_node *np);
+int lan9303_remove(struct lan9303 *chip);