drm/amd/display: Use the SPDX license identifier for dmub_replay files

Use the SPDX format for dmub_replay.c|.h files.

Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>