arm: dts: imx6ul: add usbotg aliases

This is needed to make the UMS command work again as it fails with the
following error:

BIOS> ums 0 mmc 0
UMS: LUN 0, dev 0, hwpart 0, sector 0x0, count 0x748000
g_dnl_register: failed!, error: -19
ERROR: g_dnl_register failed
at cmd/usb_mass_storage.c:179/do_usb_mass_storage()

That's because usb_setup_ehci_gadget() function is looking for the usb
device using the req_sed number.
This change makes the usb device have a req_seq number and the UMS
command work again:

BIOS> ums 0 mmc 0
UMS: LUN 0, dev 0, hwpart 0, sector 0x0, count 0x748000
CTRL+C - Operation aborted

Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>

arch/arm/dts/imx6ul.dtsi

@@ -43,6 +43,8 @@
 		spi1 = &ecspi2;
 		spi2 = &ecspi3;
 		spi3 = &ecspi4;
+		usbotg0 = &usbotg1;
+		usbotg1 = &usbotg2;
 		usbphy0 = &usbphy1;
 		usbphy1 = &usbphy2;
 	};