If tcoolthrs is configured (not the default 0), then do not force
the value of tcoolthrs=0xfffff during homing. This way, tcoolthrs
can be set to a custom value during homing.
`tpwmthrs` and `en_pwm_mode`/`en_spreadcycle` are now also
correctly restored if they were changed after startup.
Signed-off-by: Alex Voinea <voinea.dragos.alexandru@gmail.com>