Make timer definition in pin files for STM32 possible (#12874)

RemRam needs to redefine a particular timer to work correctly. The HAL did foresee this possibility and checks if the timer was already defined for either the stepper or temperature timer.

Prior to this commit the header file for the timers couldn't see those definitions in the pin file, but this commit will fix this.

Tested on an actual hardware to verify. (It wouldn't boot without it.)