ARM: BCM53016: Specify switch ports for Meraki MR32

the switch identifies itself as a BCM53012 (rev 5)...
This patch has been tested & verified on OpenWrt's
snapshot with Linux 5.10 (didn't test any older kernels).
The MR32 is able to "talk to the network" as before with
OpenWrt's SWITCHDEV b53 driver.

| b53-srab-switch 18007000.ethernet-switch: found switch: BCM53012, rev 5
| libphy: dsa slave smi: probed
| b53-srab-switch 18007000.ethernet-switch poe (uninitialized):
| PHY [dsa-0.0:00] driver [Generic PHY] (irq=POLL)
| b53-srab-switch 18007000.ethernet-switch: Using legacy PHYLIB callbacks.
| Please migrate to PHYLINK!
| DSA: tree 0 setup

Reported-by: Rafał Miłecki <[e-mail]>
Signed-off-by: Christian Lamparter <[e-mail]>
Signed-off-by: Florian Fainelli <[e-mail]>

arch/arm/boot/dts/bcm53016-meraki-mr32.dts

···
 		};
 	};
 };
+
+&srab {
+	status = "okay";
+
+	ports {
+		port@0 {
+			reg = <0>;
+			label = "poe";
+		};
+
+		port@5 {
+			reg = <5>;
+			label = "cpu";
+			ethernet = <&gmac0>;
+
+			fixed-link {
+				speed = <1000>;
+				duplex-full;
+			};
+		};
+	};
+};