Spindle speed close to minimum fix.

- When spindle speed is close to the minimum rpm, the PWM value would
be zero or lower than allowed. The computation error was caused by
setting the minimum PWM value to zero, when it should have been 1.

- Added a compiler check for minimum PWM to be greater than zero.

- Moved some of the spindle PWM macros to a more appropriate place in
the cpu_map.h.

grbl/report.c

@@ -734,7 +734,7 @@ void report_realtime_status()
       
       uint8_t sp_state = spindle_get_state();
 		  uint8_t cl_state = coolant_get_state();
-      if (sp_state || cl_state) {
+      if (sp_state | cl_state) {
         printPgmString(PSTR(",A:"));
         if (sp_state) { // != SPINDLE_STATE_DISABLE
           #ifdef VARIABLE_SPINDLE