usb: phy: ab8500-usb: restart phy during probe

Add an ab8500_usb_restart_phy() function called during probe to ensure
that the AB8500 USB phy is initialized properly even when a cable is
connected at probe time.

Without this fix subsequent host reconnections are not detected
properly.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Sakethram Bommisetti <sakethram.bommisetti@stericsson.com>
Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>