usb: otg: enable regulator only on cable/device connect

Remove the regulator enable while driver loading and enable it only when
the cable/device is connected and disable it when disconnected.

Remove the configuration of config_state and config_trans register
configuration as these registers are programmed when regulator
enable/disable is called.

Signed-off-by: Hema HK <hemahk@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>