phy: phy-stih41x-usb: Add usb phy support for STiH41x SoCs.

This driver adds support for USB (1.1 and 2.0) phy for STiH415 and
STiH416 System-On-Chips from STMicroelectronics.

Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>