Various Laser / Spindle improvements (#15335)

Marlin/src/HAL/AVR/HAL.h

@@ -395,6 +395,8 @@ inline void HAL_adc_init() {
 // AVR compatibility
 #define strtof strtod
 
+#define HAL_CAN_SET_PWM_FREQ   // This HAL supports PWM Frequency adjustment
+
 /**
  *  set_pwm_frequency
  *  Sets the frequency of the timer corresponding to the provided pin

Marlin/src/HAL/AVR/fast_pwm.cpp

@@ -23,7 +23,7 @@
 
 #include "../../inc/MarlinConfigPre.h"
 
-#if ENABLED(FAST_PWM_FAN) || SPINDLE_LASER_PWM
+#if NEEDS_HARDWARE_PWM // Specific meta-flag for features that mandate PWM
 
 #include "HAL.h"
 
@@ -278,5 +278,5 @@ void set_pwm_duty(const pin_t pin, const uint16_t v, const uint16_t v_size/*=255
   }
 }
 
-#endif // FAST_PWM_FAN || SPINDLE_LASER_PWM
+#endif // NEEDS_HARDWARE_PWM
 #endif // __AVR__