doxygen: define groups for drivers

Change-Id: Ibf6b6d8586086de5b288fee1e3b4fb1101716fe1
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/include/i2c.h b/include/i2c.h
index 42e1c60..4b7a90b 100644
--- a/include/i2c.h
+++ b/include/i2c.h
@@ -18,6 +18,13 @@
 #ifndef __DRIVERS_I2C_H
 #define __DRIVERS_I2C_H
 
+/**
+ * @brief I2C Interface
+ * @defgroup i2c_interface I2C Interface
+ * @ingroup io_interfaces
+ * @{
+ */
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -267,4 +274,9 @@
 }
 #endif
 
+/**
+ * @}
+ */
+
+
 #endif /* __DRIVERS_I2C_H */