ARM: multi_v7_defconfig: Enable stih407 usb picophy

This patch enables the picoPHY usb phy which is used by
the usb2 and usb3 host controllers when controlling usb2/1.1
devices. It is found in stih407 family SoC's from STMicroelectronics.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Maxime Coquelin <maxime.coquelin@st.com>