usb: cdns3: Fix hardware based role switch

Hardware based role switch is broken as the driver always skips it.
Fix this by registering for  SW role switch only if 'usb-role-switch'
property is present in the device tree.

Fixes: 50642709 ("usb: cdns3: core: quit if it uses role switch class")
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>