Add PDM support for circuitplay-bluefruit (#3359)

machine/nrf52840: add PDM support

Signed-off-by: Marcus Sorensen <marcus@turboio.com>

src/examples/pdm/pdm.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"fmt"
+	"machine"
+)
+
+var (
+	audio = make([]int16, 16)
+	pdm   = machine.PDM{}
+)
+
+func main() {
+	machine.BUTTONA.Configure(machine.PinConfig{Mode: machine.PinInputPulldown})
+	err := pdm.Configure(machine.PDMConfig{CLK: machine.PDM_CLK_PIN, DIN: machine.PDM_DIN_PIN})
+	if err != nil {
+		panic(fmt.Sprintf("Failed to configure PDM:%v", err))
+	}
+
+	for {
+		if machine.BUTTONA.Get() {
+			println("Recording new audio clip into memory")
+			pdm.Read(audio)
+			println(fmt.Sprintf("Recorded new audio clip into memory: %v", audio))
+		}
+	}
+}