drm/amd/display: Reduce SCDC Status Flags Definition

[Why]
Status flags definition is reduced to read
less bytes in SCDC transaction for status update.

[How]
Reduce definition of reserved bytes from 3 to 1
for status update.

Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Chris Park <chris.park@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>