w5500: initial version the driver (#788)

Thank you, @nrwiersma for working on this and @soypat for review. Now merging.

examples/w5500/main.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"machine"
+	"net"
+	"net/netip"
+	"time"
+
+	"tinygo.org/x/drivers/netdev"
+	"tinygo.org/x/drivers/w5500"
+)
+
+func main() {
+	machine.SPI0.Configure(machine.SPIConfig{
+		Frequency: 33 * machine.MHz,
+	})
+	machine.GPIO17.Configure(machine.PinConfig{Mode: machine.PinOutput})
+
+	eth := w5500.New(machine.SPI0, machine.GPIO17)
+	eth.Configure(w5500.Config{
+		MAC:        net.HardwareAddr{0xee, 0xbe, 0xe9, 0xa9, 0xb6, 0x4f},
+		IP:         netip.AddrFrom4([4]byte{192, 168, 1, 2}),
+		SubnetMask: netip.AddrFrom4([4]byte{255, 255, 255, 0}),
+		Gateway:    netip.AddrFrom4([4]byte{192, 168, 1, 1}),
+	})
+	netdev.UseNetdev(eth)
+
+	for {
+		if eth.LinkStatus() != w5500.LinkStatusUp {
+			println("Waiting for link to be up")
+
+			time.Sleep(1 * time.Second)
+			continue
+		}
+		break
+	}
+}