drm/amd/display: Write TEST_EDID_CHECKSUM_WRITE for EDID tests

Extract edid's checksum and send it back for verification if EDID_TEST
is requested.

Also added a flag for EDID checksum write in TEST_RESPONSE structure,
and simple spelling fix.

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>