ssd1306: avoid unnecessary heap allocations (#767)

* ssd1306: avoid unnecessary heap allocations

* ssd1306: extract i2c and spi bus implementations

* ssd1306: refactor tests -- show fps and heap usage

* ssd1306: bring back the lost exported methods

* Adjust examples

* Fix smoketests for ssd1306

examples/ssd1306/main_spi_thumby.go

@@ -0,0 +1,27 @@
+//go:build thumby
+
+// This initializes SSD1306 OLED display driver over SPI.
+//
+// Thumby board has a tiny built-in 72x40 display.
+//
+// As the display is built-in, no wiring is needed.
+
+package main
+
+import (
+	"machine"
+
+	"tinygo.org/x/drivers/ssd1306"
+)
+
+func newSSD1306Display() *ssd1306.Device {
+	machine.SPI0.Configure(machine.SPIConfig{})
+	display := ssd1306.NewSPI(machine.SPI0, machine.THUMBY_DC_PIN, machine.THUMBY_RESET_PIN, machine.THUMBY_CS_PIN)
+	display.Configure(ssd1306.Config{
+		Width:     72,
+		Height:    40,
+		ResetCol:  ssd1306.ResetValue{28, 99},
+		ResetPage: ssd1306.ResetValue{0, 5},
+	})
+	return display
+}