usb: phy: am335x: Use SIMPLE_DEV_PM_OPS macro

Use SIMPLE_DEV_PM_OPS macro and remove DEV_PM_OPS macro, in order
to make the code simpler.

Acked-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>