usb: twl6030-usb: make driver DT only

All users are DT-only and it makes no sense to keep
unused code

Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Nicolae Rosia <Nicolae_Rosia@mentor.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>