dt-bindings: usb: Add documentation for AM62 USB Wrapper module

Add bindings for the TI's AM62 wrapper module for the Synopsys USBSS-DRD
controller.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Link: https://lore.kernel.org/r/20220414103211.16202-2-a-govindraju@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>