[NUCLEO_F401RE] Remove PB_11 pin.
[NUCLEO_L152RE] Change us_ticker timer (32-bit one)
[NUCLEO_F401RE] Change us_ticker timer (32-bit one)

Remove also the disable/enable timer update IT in sleep (no more
necessary).
Merge pull request #177 from bcostm/master

Change us_ticker timer (32-bit) on Nucleo L152RE and F401RE