linux-phytec-ti

dt-bindings: add binding for USBSS-DRD controller.

This patch aim at documenting USB related dt-bindings for the
Cadence USBSS-DRD controller.

Signed-off-by: Pawel Laszczak <pawell@cadence.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>