trx: handle synchronous TRX control callbacks in provision FSM
Set *_sent flags before issuing TRX control commands to ensure
correct state when responses are delivered synchronously
(e.g. WebUSB callback path)
Also guard FSM state handling in st_open_poweroff() to avoid
duplicate transitions if state was already changed by a
synchronous response
No functional change for asynchronous (socket-based) backends
Change-Id: I50c95e3796839e9fe721bff6f96fed4c490c6018
