drm/amd/display: Remove MALL function from DCN3.1

[why]
DCN31 doesn't have MALL in DMUB so to avoid sending unknown commands to
DMUB just remove the function pointer.

[how]
Remove apply_idle_power_optimizations from function pointers structure
for DCN31

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>