usb: gadget: mv_u3d: make mv_u3d_pm_ops static

Make mv_u3d_pm_ops static because mv_u3d_pm_ops is not exported.
Also, CONFIG_PM_SLEEP is used to remove unnecessary ifdefs.

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