If asynchronous tranfers are supported, then there must also be a mechanism to cancel the pending transfer

USB hub fixes.  Mostly dealing with setting the hub function address at the right time and powering up downstream ports

Fix USB hub bugs: Don't allocate port EP0 until needed, otherwise run out of endpoints; using wrong pointer to access child endpoint array in a few places

sem_wait(): Missing comma on debug statement caused compile error with DEBUG on.  Why hasn't that been noted before?

STM32 RTC counter: Include enable/disable backup domain within critical section.  Per recommendtion of Alexander Oryshchenko.