ARM: dts: bcm283x: Add dtsi for OTG mode

The Raspberry Pi Zero also supports OTG mode. So provide a dtsi file
to configure the USB interface accordingly. The fifo sizes are optimized
for device endpoint 6 and 7 with the maximum of 768.
Signed-off-by: NStefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: NEric Anholt <eric@anholt.net>

arch/arm/boot/dts/bcm283x-rpi-usb-otg.dtsi

+&usb {
+	dr_mode = "otg";
+	g-rx-fifo-size = <256>;
+	g-np-tx-fifo-size = <32>;
+	/*
+	 * According to dwc2 the sum of all device EP
+	 * fifo sizes shouldn't exceed 3776 bytes.
+	 */
+	g-tx-fifo-size = <256 256 512 512 512 768 768>;
+};