dts: bindings: add new bindings snps,dwc2 and st,stm32f4-fsotg

Although snps,designware-usb bindings already exist, this one is
prolematic. Compatible is too general and does not reflect
the actual controller IP. It has Zephyr-specific properties,
but has no zephyr prefix. It forces properties that are not
necessary for this controller. We start here with new bare minimum
properties for DesignWare OTG USB 2.0 controller.

The STM32F4 SoC family USB controllers, which are also implement
DesignWare OTG USB 2.0 IP, can also be used with existing drivers,
but require certain quirks. To use these we need special compatible.

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>