TIM8 correctly. Software serial conficted with parallel PWM input. Fixed
crash due to incorrect timerConfig index calculation code.
The crash occurred when capture compare interrupt handlers attempted to
call an invalid callback.
Note: the crash does not affect existing baseflight code since the
formula is OK when using a 2 dimensional array with equal dimensions.
Formula details here:
https://docs.google.com/spreadsheets/d/1UuxnC0VKiprvt1wt3KXffefEWJUb_-ILFLQuP377Anw
Achieved by renaming MAX_MOTORS to MAX_PWM_MOTORS
Disambiguate MAX_MOTORS and MAX_SUPPORTED_SERVOS
Achieved by renaming MAX_SERVOS to MAX_PWM_SERVOS
It now shows there is a dependency on the pwm driver if MAX_PWM_* is
used.
Coupled pwm_common and timer_common by using USABLE_TIMER_CHANNEL_COUNT
since the current pwm driver and timer driver is only usable by the
STM32F103.