Deduplicate create_image from Copy/Fill image tests (#2262)

1. Remove duplicate `create_image` code that is in both clFillImage and
clCopyImage test directories.
2. Unify how pitch buffer's memory is deallocated; The buffer can be
allocated with either `malloc` or `align_malloc` and the free function
is pre-set in `pitch_buffe_data`'s member variable `free_fn` and used
when the buffer is deallocated. With this, the change removes
`is_aligned` conditional variable that was used to select the
appropriate free function.

Signed-off-by: Michael Rizkalla <michael.rizkalla@arm.com>

test_conformance/images/common.h

@@ -50,4 +50,9 @@ int get_format_list(cl_context context, cl_mem_object_type imageType,
                     cl_mem_flags flags);
 size_t random_in_ranges(size_t minimum, size_t rangeA, size_t rangeB, MTdata d);
 
+clMemWrapper create_image(cl_context context, cl_command_queue queue,
+                          BufferOwningPtr<char> &data,
+                          image_descriptor *imageInfo, bool enable_pitch,
+                          bool create_mipmaps, int *error);
+
 #endif // IMAGES_COMMON_H