kinetis: lptmr reload instead of spinning
kinetis: lptmr reload instead of spinning

Spinning for the correct time has the side effect that it may cause
infinite recursion if the callback function calls timer_set.

timer_set->callback->...->timer_set->callback->...->timer_set-> infinity

In theory, the drawback is that the callback for very short timeouts
(<2 lptmr ticks) may be delayed up to 2 lptmr ticks (61 µs)

In practice however, tests performed using tests/bench_timers shows that
this change only affects the accuracy of the timer target when timer_set
is called with a timeout of 0, which results in a delay of 30 µs.

jasonatran/RIOT,smlng/RIOT,cladmi/RIOT,cladmi/RIOT,toonst/RIOT,ant9000/RIOT,ant9000/RIOT,josephnoir/RIOT,OlegHahm/RIOT,aeneby/RIOT,OlegHahm/RIOT,yogo1212/RIOT,OlegHahm/RIOT,kYc0o/RIOT,rfuentess/RIOT,cladmi/RIOT,aeneby/RIOT,kYc0o/RIOT,yogo1212/RIOT,rfuentess/RIOT,yogo1212/RIOT,yogo1212/RIOT,mtausig/RIOT,yogo1212/RIOT,rfuentess/RIOT,OlegHahm/RIOT,toonst/RIOT,mtausig/RIOT,josephnoir/RIOT,mtausig/RIOT,josephnoir/RIOT,OTAkeys/RIOT,smlng/RIOT,miri64/RIOT,RIOT-OS/RIOT,aeneby/RIOT,ant9000/RIOT,authmillenon/RIOT,basilfx/RIOT,toonst/RIOT,authmillenon/RIOT,miri64/RIOT,RIOT-OS/RIOT,miri64/RIOT,OlegHahm/RIOT,mtausig/RIOT,x3ro/RIOT,OTAkeys/RIOT,jasonatran/RIOT,kYc0o/RIOT,rfuentess/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,basilfx/RIOT,cladmi/RIOT,kaspar030/RIOT,basilfx/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,x3ro/RIOT,kaspar030/RIOT,kaspar030/RIOT,kaspar030/RIOT,authmillenon/RIOT,authmillenon/RIOT,x3ro/RIOT,smlng/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,kYc0o/RIOT,aeneby/RIOT,toonst/RIOT,yogo1212/RIOT,jasonatran/RIOT,basilfx/RIOT,jasonatran/RIOT,kYc0o/RIOT,authmillenon/RIOT,cladmi/RIOT,miri64/RIOT,OTAkeys/RIOT,smlng/RIOT,josephnoir/RIOT,miri64/RIOT,basilfx/RIOT,OTAkeys/RIOT,mtausig/RIOT,OTAkeys/RIOT,ant9000/RIOT,x3ro/RIOT,x3ro/RIOT,aeneby/RIOT,josephnoir/RIOT,rfuentess/RIOT,toonst/RIOT,ant9000/RIOT,smlng/RIOT