ARM: dts: stm32: enable USB Host EHCI on stm32mp135f-dk

USBH Host EHCI controller manages the USB High-Speed hub controller IC
offering Type-A CN5 & CN6 connectors available on stm32mp135f-dk.
USB Host OHCI controller doesn't need to be enabled as Full-Speed and
Low-Speed traffic will be managed by the hub.
This USB2514B onboard hub is supplied by a 3v3 PMIC regulator.

Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>