Fix initialization of GpioController in Atom and M5Stick (#193)

Author: josesimoes

AtomCommon/AtomBase.cs

@@ -53,7 +53,18 @@ public static GpioButton Button
         /// <summary>
         /// Gets the main <see cref="GpioController"/>.
         /// </summary>
-        public static GpioController GpioController => _gpio;
+        public static GpioController GpioController
+        {
+            get
+            {
+                if (_gpio is null)
+                {
+                    _gpio = new();
+                }
+
+                return _gpio;
+            }
+        }
 
         /// <summary>
         /// Gets <see cref="DacChannel"/> connected to GPIO 25.

nanoFramework.M5StickCommon/M5StickCBase.cs

@@ -134,7 +134,18 @@ public static Pcf8563 RealTimeClock
         /// <summary>
         /// Gets the main GPIO Controller.
         /// </summary>
-        public static GpioController GpioController => _gpio;
+        public static GpioController GpioController
+        {
+            get
+            {
+                if (_gpio is null)
+                {
+                    _gpio = new();
+                }
+
+                return _gpio;
+            }
+        }
 
 #if M5STICKC
         static M5StickC()