metal/ios: add UNITY_NO_DXT5nm path for normal maps

Assets/ScriptableRenderPipeline/ShaderLibrary/SampleUVMappingInternal.hlsl

 // TODO: Handle BC5 format, currently this code is for DXT5nm - After the change, rename this function UnpackNormalmapRGorAG
 // This version is use for the base normal map
 #define ADD_NORMAL_FUNC_SUFFIX(Name) Name
+#if defined(UNITY_NO_DXT5nm)
+#define UNPACK_NORMAL_FUNC UnpackNormalRGB
+#define UNPACK_DERIVATIVE_FUNC UnpackDerivativeNormalRGB
+#else
+#endif
 #include "SampleUVMappingNormalInternal.hlsl"
 #undef ADD_NORMAL_FUNC_SUFFIX
 #undef UNPACK_NORMAL_FUNC
 #define ADD_NORMAL_FUNC_SUFFIX(Name) Name##AG
+#if defined(UNITY_NO_DXT5nm)
+#define UNPACK_NORMAL_FUNC UnpackNormalRGB
+#define UNPACK_DERIVATIVE_FUNC UnpackDerivativeNormalRGB
+#else
+#endif
 #include "SampleUVMappingNormalInternal.hlsl"
 #undef ADD_NORMAL_FUNC_SUFFIX
 #undef UNPACK_NORMAL_FUNC