Most of the conformance tests read a pixel value and assert that it
matches a known value. However they were all doing this with slightly
different methods. This adds a common test_utils_check_pixel function
which they now all use. The function takes an x and y coordinate and a
32-bit value representing the color. It is assumed that writing a
known color is most convenient as an 8 digit hex sequence which this
function allows. There is also a test_utils_check_pixel_rgb function
wrapper which takes the components as separate arguments. This is more
convenient when the expected color is also calculated by the test.
Reviewed-by: Robert Bragg <robert@linux.intel.com>
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