dt-bindings: marvell,prestera: Add description for device-tree bindings

Add brief description how to configure base mac address binding in
device-tree.

Describe requirement for the PCI port which is connected to the ASIC, to
allow access to the firmware related registers.

Signed-off-by: Vadym Kochan <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/devicetree/bindings/net/marvell,prestera.txt

···
 	ranges = <0 MBUS_ID(0x08, 0x00) 0 0x100000>;
 	reg = <MBUS_ID(0x08, 0x00) 0 0x100000>;
 };
+
+Marvell Prestera SwitchDev bindings
+-----------------------------------
+Optional properties:
+- compatible: must be "marvell,prestera"
+- base-mac-provider: describes handle to node which provides base mac address,
+	might be a static base mac address or nvme cell provider.
+
+Example:
+
+eeprom_mac_addr: eeprom-mac-addr {
+       compatible = "eeprom,mac-addr-cell";
+       status = "okay";
+
+       nvmem = <&eeprom_at24>;
+};
+
+prestera {
+       compatible = "marvell,prestera";
+       status = "okay";
+
+       base-mac-provider = <&eeprom_mac_addr>;
+};
+
+The current implementation of Prestera Switchdev PCI interface driver requires
+that BAR2 is assigned to 0xf6000000 as base address from the PCI IO range:
+
+&cp0_pcie0 {
+	ranges = <0x81000000 0x0 0xfb000000 0x0 0xfb000000 0x0 0xf0000
+		0x82000000 0x0 0xf6000000 0x0 0xf6000000 0x0 0x2000000
+		0x82000000 0x0 0xf9000000 0x0 0xf9000000 0x0 0x100000>;
+	phys = <&cp0_comphy0 0>;
+	status = "okay";
+};