PID loop improvements (#14746)

* Fix macro evaluation in `temperature.cpp`
* Improve bed PID, PID debug output
* Add min PID power define

config/examples/Formbot/T_Rex_2+/Configuration.h

@@ -542,7 +542,7 @@
 #define MAX_BED_POWER 255 // limits duty cycle to bed; 255=full current
 
 #if ENABLED(PIDTEMPBED)
-
+  //#define MIN_BED_POWER 0
   //#define PID_BED_DEBUG // Sends debug data to the serial port.
 
   #ifdef ROXYs_TRex