ARM: dts: stm32: add phy-names to usbotg_hs on stm32mp157c-ev1

phy-names is required by usbotg_hs driver to get the phy, otherwise, it
considers that there is no phys property.

Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>