drm/amd/display: Enable eDP ILR on DCN2.1

[WHY]
Enable feature for 21.40

Reviewed-by: Sung Lee <Sung.Lee@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>