Correct TuningLevel enumeration values

According to the header description - include/armnn/IRuntime.hpp, Each level should have below value.
-----------------------------------------------------------------------------------------------------
"TuningLevel" : int [0..3] (0=UseOnly(default) | 1=RapidTuning | 2=NormalTuning | 3=ExhaustiveTuning)
-----------------------------------------------------------------------------------------------------

And also src/backends/cl/ClBackendContext.cpp uses below enumeration values internally
for the tuning level,
----------------------
enum class TuningLevel                                                          
{                                                                               
    None,                                                                       
    Rapid,                                                                      
    Normal,                                                                     
    Exhaustive                                                                  
};
----------------------

So this patch corrects TuningLevel enumeration values - which is exposed to user - to be consistent
with ones internally used.

Change-Id: I9a8aeea0115579bfd16cbe01f39183b96329cdfd
Signed-off-by: Inki Dae <inki.dae@samsung.com>
diff --git a/include/armnn/IRuntime.hpp b/include/armnn/IRuntime.hpp
index 4114c99..9122089 100644
--- a/include/armnn/IRuntime.hpp
+++ b/include/armnn/IRuntime.hpp
@@ -203,9 +203,9 @@
 
     enum class TuningLevel
     {
-        Rapid = 0,
-        Normal = 1,
-        Exhaustive = 2
+        Rapid = 1,
+        Normal = 2,
+        Exhaustive = 3
     };
 
     /// Creates an IClTunedParameters with the given mode.