Ignore padding bits in clCopyImage/clFillImage testing (#1184)

The CL_UNORM_SHORT_555 and CL_UNORM_INT_101010 formats contain padding
bits which need to be ignored in clCopyImage and clFillImage testing.

For clFillImage tests, padding was not ignored for the CL_UNORM_SHORT_555
format, and was ignored for CL_UNORM_INT_101010 by modifying actual and
reference data.  For clCopyImage tests, padding was not ignored, both for
CL_UNORM_SHORT_555 and for CL_UNORM_INT_101010.

Fix this by adding a new compare_scanlines() function, which is used for
both of these formats, and does not modify the actual or reference data.

Signed-off-by: Stuart Brady <stuart.brady@arm.com>

test_common/harness/imageHelpers.h

@@ -139,6 +139,9 @@ void print_first_pixel_difference_error(size_t where, const char *sourcePixel,
                                         image_descriptor *imageInfo, size_t y,
                                         size_t thirdDim);
 
+size_t compare_scanlines(const image_descriptor *imageInfo, const char *aPtr,
+                         const char *bPtr);
+
 void get_max_sizes(size_t *numberOfSizes, const int maxNumberOfSizes,
                    size_t sizes[][3], size_t maxWidth, size_t maxHeight,
                    size_t maxDepth, size_t maxArraySize,