ARM: dts: DRA7: Move USB_OTG 4 to dra74x.dtsi

The 4th USB controller instance present only on the DRA74x family of
devices so move it there.

Signed-off-by: Roger Quadros <rogerq@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>