stm32mp1: remove CONFIG_USB_DWC2, HOST support for USBO

Remove the HOST support for STM32MP1 USBO device = OTG DWC2.
The current DWC2 driver have no dynamic detection of device,
So it is dangerous to have start 3V3 when PC is
connected to the micro USB connector.

=> it is preferable to have only DEVICE support
   CONFIG_USB_GADGET_DWC2_OTG for OTG port

See DWC3 driver for clean dual role support...

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>