Adding scroll functionality for ili9341

[bgould]

This PR adds a method for setting the vertical scroll address in the ILI9341 driver.

[conejoninja]

I would also add SetScrollArea and StopScroll

I found that ST7735 do also have scroll functionality (and probably ST7789 too). I used the same register name and functions and added 2 more to specify which area to scroll and to return to normal, althought SetScroll(0) works too

// SetScrollWindow sets an area to scroll with fixed top and bottom parts of the display
func (d *Device) SetScrollArea(topFixedArea, bottomFixedArea int16) {
	d.Command(VSCRDEF)
	d.Tx([]uint8{
		uint8(topFixedArea >> 8), uint8(topFixedArea),
		uint8(d.height - topFixedArea - bottomFixedArea>>8), uint8(d.height - topFixedArea - bottomFixedArea),
		uint8(bottomFixedArea >> 8), uint8(bottomFixedArea)},
		false)
}

// SetScroll sets the vertical scroll address of the display.
func (d *Device) SetScroll(line int16) {
	d.Command(VSCRSADD)
	d.Tx([]uint8{uint8(line >> 8), uint8(line)}, false)
}

// SpotScroll returns the display to its normal state
func (d *Device) StopScroll() {
	d.Command(NORON)
}

[deadprogram]

@bgould not sure if you saw the comment from @conejoninja above?

[bgould]

I would also add SetScrollArea and StopScroll

@conejoninja Thanks, that is a great idea, I will get these added.