Re-added aht21 folder

Fixed folder naming issues.

Author: thussaiththelaw

components/i2c/aht21/definition.json

@@ -0,0 +1,6 @@
+{
+    "vendor": "Hiletgo",
+    "displayName": "aht21",
+    "i2cAddresses": [ "0x38"],
+    "subcomponents": [ "ambient-temp", "ambient-temp-fahrenheit", "humidity"]
+}