doc: dt-binding: cdns,usb3: Add interrupt-names property under required

In the driver the interrupts are fetched by name. Therefore, add
interrupt names in the list of required properties

Fixes: 68989fe1 ("dt-bindings: usb: Convert cdns-usb3.txt to YAML schema")
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Link: https://lore.kernel.org/r/20210528060657.29100-1-a-govindraju@ti.com


Signed-off-by: Peter Chen <peter.chen@kernel.org>