usb: phy: twl4030: fix cold plug on OMAP3

Having twl4030_usb_phy_init() (detects if a cable is connected before
twl4030 is probed) in twl4030 probe makes cable connect events to be
missed by musb glue, since it gets loaded after twl4030. Having
twl4030_usb_phy_init as a usb_phy ops lets twl4030_usb_phy_init to be
called when glue is ready.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Tested-by: Grazvydas Ignotas <notasas@gmail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>