cores: Add API guards to overloads.h for consistent with other parts

Add #pragma once and align analogReadResolution() /
analogWriteResolution() declaration guards with existing CONFIG_* usage.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>

Author: soburi

cores/arduino/overloads.h

@@ -13,5 +13,14 @@ void analogWrite(enum dacPins pinNumber, int value);
 #endif
 
 // In c++ mode, we also provide analogReadResolution and analogWriteResolution getters
+#ifdef CONFIG_ADC
+
 int analogReadResolution();
+
+#endif
+
+#if defined(CONFIG_PWM) || defined(CONFIG_DAC)
+
 int analogWriteResolution();
+
+#endif