ARM: dts: am43xx clock data

Add USB and USB PHY reference clock data

Signed-off-by: George Cherian <george.cherian@ti.com>
Acked-by: Roger Quadros <rogerq@ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>
[tony@atomide.com: tabified]
Signed-off-by: Tony Lindgren <tony@atomide.com>