Fix stm32 cputimer initialization
Fix stm32 cputimer initialization

Peripheral initialization unification cut out cpu timer initialization.
So all STM32 BSP are not working correctly.
Code:
    rc = os_cputime_init(MYNEWT_VAL(OS_CPUTIME_FREQ));
    assert(rc == 0);
was removed from all BSPs but it was not added to stm32_periph.c

mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core,mlaz/mynewt-core