usb: phy: msm: Enable deferred driver probing

Using platform_driver_probe() prevent driver from requesting
probe deferral. Fix this.

While at that, also switch to module_platform_driver() and
remove __init annotation from probe().

Signed-off-by: Ivan T. Ivanov <iivanov@mm-sol.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>