STM32: moved timer_ic_set_polarity from timer_common_all to
f1/timer.
Added timer_ic_set_polarity to timer_common_f24 with
the enum tim_ic_pol now including trigger on both edges.
Changed timer_slave_set_polarity to use enum tim_et_pol
rather than tim_ic_pol.

In response to suggestion of stinkydiver73 on 24 March that
timers in all families have an option for triggers on both
edges, except F1.
[stm32] usart6 for F2/F4
[stm32] update doxy for usart_set_baudrate
Merge remote-tracking branch 'upstream/master'