[generators] gen_airframe: don't force float if unit = code_unit
[fixedwing] if USE_BARO_BOARD: separate baro timer

before baro_periodic was running at PERIODIC_FREQUENCY in sensors_task,
which is too fast for ms5611 if periodic freq is > 100Hz
[lpc21] don't override T0CCR values when setting ppm and trig_ext
possibility to pass ref to paparazzi_version
[baro_board] make configure work for BARO_PERIODIC_FREQUENCY (needed to use define before)
[sys_time] maximum of 16 sys_time timers by default (was 8)

actually makes the baro periodic timer (for BARO_BOARD) usable by default on fixedwings
[ins] alt_float: if USE_BARO_BOARD, dt is 1/BARO_PERIODIC_FREQUENCY
[baro_board] ms5611, error if BARO_PERIODIC_FREQ is over 100