[Why & How]
DCN guard is not necessary for DP2.x relevant logic.
Drop them.

v2: squash in fix for misplaced #endif (Alex)
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: NRodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: NJerry Zuo <Jerry.Zuo@amd.com>
Acked-by: NRodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: NWenjing Liu <wenjing.liu@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>