USB2 port can be operated in dual-role mode but till we
have dual-role support in dwc3 driver let's limit this
port to peripheral mode.

If we don't do so it defaults to host mode. USB1 port
is meant for host only operation and we don't want
both ports in host only mode.
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>