Generic Address Space: Skip tests utlilising SVM on devices that do n… (#712)

* Harness: Added an option for a test to skip itself.

New condtion in callSingleTestFunction. This allows a test to return TEST_SKIP if the device does not support the requested test.

* Split generic_ptr_to_host_mem into two tests.

The old generic_ptr_to_host_mem test tests two different device capabilities (SVM and not SVM). This is a prerequisite for the following commit.

* Generic Address Space: Skip tests utlilising SVM on devices that do not support SVM.

Where a device does not support SVM, do not run the generic address space test(s) that rely on SVM.

test_common/harness/threadTesting.h

@@ -23,6 +23,7 @@
 #endif
 
 #define TEST_NOT_IMPLEMENTED        -99
+#define TEST_SKIPPED_ITSELF         -100
 
 typedef int (*basefn)(cl_device_id deviceID, cl_context context, cl_command_queue queue, int num_elements);
 extern int test_threaded_function( basefn fnToTest, cl_device_id device, cl_context context, cl_command_queue queue, int numElements );