[SYCL] This PR adds the minimum modifications to the Eigen unsupported module required to run it on devices supporting SYCL.

* Abstracting the pointer type so that both SYCL memory and pointer can be captured.
* Converting SYCL virtual pointer to SYCL device memory in Eigen evaluator class.
* Binding SYCL placeholder accessor to command group handler by using bind method in Eigen evaluator node.
* Adding SYCL macro for controlling loop unrolling.
* Modifying the TensorDeviceSycl.h and SYCL executor method to adopt the above changes.

unsupported/test/cxx11_tensor_morphing.cpp

@@ -51,7 +51,8 @@ static void test_static_reshape() {
 
   // New dimensions: [2, 3, 7]
   Eigen::IndexList<type2index<2>, type2index<3>, type2index<7>> dim;
-  Tensor<float, 3> reshaped = tensor.reshape(dim);
+  Tensor<float, 3> reshaped = tensor.reshape(static_cast<Eigen::DSizes<long,3>>(dim));
+  
 
   for (int i = 0; i < 2; ++i) {
     for (int j = 0; j < 3; ++j) {