Add support for setting framerate, vsync pause, and reading scanline data.

- FrameRate option sets device framerates from 39-111Hz
- VSyncLines option adjusts device vsync pause using st7789 "porch control" feature
- Added Rx(cmd, bytes[]) to support retrieving scanline timing data over SPI
- Added Sync functions to support syncronization of animation to vertical scanline timing
- Minor adjustments to Configure to clear screen memory before display is visible

examples/st7789/main.go

@@ -9,12 +9,37 @@ import (
 )
 
 func main() {
+
+	// Example configuration for Adafruit Clue
+	// machine.SPI1.Configure(machine.SPIConfig{
+	//	Frequency: 8000000,
+	//	SCK:       machine.TFT_SCK,
+	//	SDO:       machine.TFT_SDO,
+	//	SDI:       machine.TFT_SDO,
+	//	Mode:      0,
+	// })
+	// display := st7789.New(machine.SPI1,
+	//	machine.TFT_RESET,
+	//	machine.TFT_DC,
+	//	machine.TFT_CS,
+	//	machine.TFT_LITE)
+
 	machine.SPI0.Configure(machine.SPIConfig{
 		Frequency: 8000000,
-		Mode:      3,
+		Mode:      0,
+	})
+	display := st7789.New(machine.SPI0,
+		machine.P6, // TFT_RESET
+		machine.P7, // TFT_DC
+		machine.P8, // TFT_CS
+		machine.P9) // TFT_LITE
+
+	display.Configure(st7789.Config{
+		Rotation:   st7789.NO_ROTATION,
+		RowOffset:  80,
+		FrameRate:  st7789.FRAMERATE_111,
+		VSyncLines: st7789.MAX_VSYNC_SCANLINES,
 	})
-	display := st7789.New(machine.SPI0, machine.P6, machine.P7, machine.P8, machine.P9)
-	display.Configure(st7789.Config{Rotation: st7789.NO_ROTATION})
 
 	width, height := display.Size()