sdcard: add support for spi sdcard driver

examples/sdcard/console/feather-m4.go

@@ -0,0 +1,23 @@
+// +build feather_m4 feather_m4_can
+
+package main
+
+import (
+	"machine"
+)
+
+func init() {
+	spi = machine.SPI0
+	spi.Configure(machine.SPIConfig{
+		SCK:       machine.SPI0_SCK_PIN,
+		SDO:       machine.SPI0_SDO_PIN,
+		SDI:       machine.SPI0_SDI_PIN,
+		Frequency: 24000000,
+		LSBFirst:  false,
+		Mode:      0, // phase=0, polarity=0
+	})
+
+	csPin = machine.D10
+
+	ledPin = machine.LED
+}