Added CM4 model check to IsPi4 (#2125)

CM4 needs to be handled the same way as a pi4. Right now, due to the device model of a CM4 being "Raspberry Pi Computer Module 4" it is being treated as a pi3. This causes a problem with the pin mapping and prevents the CM4 from having it's input/output and pullup/pulldown changed on OpenPin().

src/System.Device.Gpio/System/Device/Gpio/Drivers/RaspberryPi3LinuxDriver.cs

@@ -722,7 +722,7 @@ internal unsafe class RaspberryPi3LinuxDriver : GpioDriver
                 if (File.Exists(ModelFilePath))
                 {
                     string model = File.ReadAllText(ModelFilePath, Text.Encoding.ASCII);
-                    if (model.Contains("Raspberry Pi 4"))
+                    if (model.Contains("Raspberry Pi 4") || model.Contains("Raspberry Pi Compute Module 4"))
                     {
                         IsPi4 = true;
                     }