PiOS_Servo: Allows the PWM output to scale to very long periods.
Actuator: 1) Several formatting and comment fixes requested in review.
2) Fixed &= which should have been = &&.
3) Exit without setting timer when calling prohibited TIM6 and TIM7
4) Check for successful memory allocation.
PiOS: Updated F1 targets to specifically define the APB1 and APB2 speeds,
as is done in the F3 and F4 targets.
PiOS Servo: Set prescalers correctly

On the STM32 microcontrollers, the timer clocks are doubled if the timer
clock prescaler is other than 1.
Merge pull request #982 from kubark42/fix-actuator-period

Fix actuator period to allow for lower output rates than 16Hz