Documentation

This patch adds phy tranceiver 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.

Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>