Implement idle mode for ILI9163

Support of idle mode.
Based on ILI9163 datasheet:
https://www.rockbox.org/wiki/pub/Main/SonyNWZE370/ILI9163.pdf

TFT_Drivers/ILI9163_Defines.h

@@ -61,6 +61,8 @@
 #define TFT_INVOFF  0x20
 #define TFT_INVON   0x21
 
-#define TFT_NORON 0x13 //normal mode
-#define TFT_PTLON 0x12 //partial mode
-#define TFT_PTLAR 0x30 //partial area
+#define TFT_NORON  0x13 //normal mode
+#define TFT_PTLON  0x12 //partial mode
+#define TFT_PTLAR  0x30 //partial area
+#define TFT_IDMOFF 0x38 //idle mode off
+#define TFT_IDMON  0x39 //idle mode on

TFT_eSPI.cpp

@@ -3273,6 +3273,20 @@ void TFT_eSPI::setPartialArea(int16_t startLine, int16_t endLine)
 #endif
 }
 
+/***************************************************************************************
+** Function name:           setIdleMode
+** Description:             enables/disables "idle" mode, where color expression is reduced to 8 colors
+**                          can be used with partial mode, further reducing power consumption
+***************************************************************************************/
+void TFT_eSPI::setIdleMode(bool mode)
+{
+#ifdef ILI9163_DRIVER
+  spi_begin();
+  writecommand(mode ? TFT_IDMON : TFT_IDMOFF);
+  spi_end();	
+#endif
+}
+
 /***************************************************************************************
 ** Function name:           write
 ** Description:             draw characters piped through serial stream

TFT_eSPI.h

@@ -355,9 +355,11 @@ class TFT_eSPI : public Print {
 
            setRotation(uint8_t r),
            invertDisplay(boolean i),
-		   
+           
            setPartialMode(bool mode),
            setPartialArea(int16_t startLine, int16_t endLine),
+           
+           setIdleMode(bool mode),
 
            drawCircle(int32_t x0, int32_t y0, int32_t r, uint32_t color),
            drawCircleHelper(int32_t x0, int32_t y0, int32_t r, uint8_t cornername, uint32_t color),