usb: phy: ab8500-usb: adopt pinctrl support

Amend the ab8500-usb driver to optionally take a pin control handle and
set the state of the pins to "default" on ab8500_usb_phy_enable and to
"sleep" on ab8500_usb_phy_disable.

The pinctrl handle is released on ab8500_usb_phy_disable because USB
pins are shared with ab8505_micro_usb_iddet driver.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Fabio Baltieri <fabio.baltieri@linaro.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>