Add check for Read-Write images support (#965)

* Fix enqueue_flags test to use correct barrier type.

Currently, enqueue_flags test uses CLK_LOCAL_MEM_FENCE.
Use CLK_GLOBAL_MEM_FENCE instead as all threads across work-groups
need to wait here.

* Add check for support for Read-Wrie images

Read-Write images have required OpenCL 2.x.
Read-Write image tests are already being skipped
for 1.x devices.
With OpenCL 3.0, read-write images being optional,
the tests should be run or skipped
depending on the implementation support.

Add a check to decide if Read-Write images are
supported or required to be supported depending
on OpenCL version and decide if the tests should
be run on skipped.

Fixes issue #894

* Fix formatting in case of Read-Write image checks.

Fix formatting in case of Read-write image checks.
Also, combine two ifs into one in case of
kerne_read_write tests

* Fix some more formatting for RW-image checks

Remove unnecessary spaces at various places.
Also, fix lengthy lines.

test_conformance/images/samplerlessReads/test_read_2D_array.cpp

@@ -176,6 +176,11 @@ int test_read_image_set_2D_array( cl_device_id device, cl_context context, cl_co
 
     int error;
 
+    if (gTestReadWrite && checkForReadWriteImageSupport(device))
+    {
+        return TEST_SKIPPED_ITSELF;
+    }
+
     clProgramWrapper program;
     clKernelWrapper kernel;