Added float16 support for constant op (#3039)

* Added float16 support for constant op

* Fix Compilation issue.

* Style.

src/ngraph/builder/make_constant.hpp

@@ -19,6 +19,7 @@
 #include "ngraph/node.hpp"
 #include "ngraph/op/broadcast.hpp"
 #include "ngraph/op/constant.hpp"
+#include "ngraph/type/float16.hpp"
 
 namespace ngraph
 {
@@ -40,6 +41,13 @@ namespace ngraph
                 val = std::make_shared<ngraph::op::Constant>(
                     type, ngraph::Shape{}, std::vector<double>{static_cast<double>(num)});
             }
+            else if (type == element::f16)
+            {
+                val = std::make_shared<ngraph::op::Constant>(
+                    type,
+                    ngraph::Shape{},
+                    std::vector<ngraph::float16>{ngraph::float16(static_cast<float>(num))});
+            }
             else if (type == element::i64)
             {
                 val = std::make_shared<ngraph::op::Constant>(