[STM32F0] add support of autotrimming HSI to USB SOF frames

Signed-off-by: Frantisek Burian <BuFran@seznam.cz>
[STM32F0] Add support functions for USB clock setup in F072 chips.

There is remaining an issue with PREDIV connected just after clock multiplexer (only F072). This should be fixed in another commit.
Commonize USB
[USB] Add commonized driver for USB STM32F0 line (prepared for L0)

Pioneer work originally by Kuldeep Singh Dhaka. Code reformatted.

Signed-off-by: Frantisek Burian <BuFran@seznam.cz>