Since dcn20 and dcn21 are under dcn1 it doesnt make sense to
have it named dcn1.

Change it to "dcn" to make it generic
Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>