Improved support for panelolu2 encoder and buzzer

I added #define for LCD_FEEDBACK_FREQUENCY_HZ and
LCD_FEEDBACK_FREQUENCY_DURATION_MS  which is used to alter the default
buzzer sound.

When selecting Panelolu2 in configuration.h:
- it automatically sets the correct ENCODER_PULSES_PER_STEP and
ENCODER_STEPS_PER_MENU_ITEM.
- if LCD_USE_I2C_BUZZER is defined it will also set the default
LCD_FEEDBACK_FREQUENCY_HZ and LCD_FEEDBACK_FREQUENCY_DURATION_MS

When selecting the sanguinololu 1284p the following is true:
- its now enables  LARGE_FLASH
- It enables the gcode M300 when the panelolu2 LCD_USE_I2C_BUZZER is
defined

Marlin/pins.h

@@ -971,6 +971,10 @@
 #undef MOTHERBOARD
 #define MOTHERBOARD 6
 #define SANGUINOLOLU_V_1_2
+
+#if defined(__AVR_ATmega1284P__)
+	#define LARGE_FLASH true
+#endif
 #endif
 #if MOTHERBOARD == 6
 #define KNOWN_BOARD 1