zynq-topic-miami.dts: Add usbotg0 alias to make USB actually work

Fixes the following problem:
zynq-uboot> run dfu_ram
Setting bus to 1
g_dnl_register: failed!, error: -19

The cause appears to be that the USB framework is looking for a usbotg aliases,
so add the alias to point to our USB device.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>