phy: stm32: add support for STM32 USB PHY Controller (USBPHYC)

This patch adds phy transceiver driver for STM32 USB PHY Controller
(USBPHYC) that provides dual port High-Speed phy for OTG (single port)
and EHCI/OHCI host controller (two ports).
One port of the phy is shared between the two USB controllers through
a UTMI+ switch.

[fengguang.wu@intel.com: Make stm32_usbphyc_get_pll_params() to be static]
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>