drm/amd/display: undo clearing of z10 related function pointers

[Why]
Z10 and S0i3 have some shared path. Previous code clean up ,
incorrectly removed these pointers, which breaks s0i3 restore

[How]
Do not clear the function pointers based on Z10 disable.

Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn31/dcn31_init.c

@@ -153,9 +153,4 @@ void dcn31_hw_sequencer_construct(struct dc *dc)
 		dc->hwss.init_hw = dcn20_fpga_init_hw;
 		dc->hwseq->funcs.init_pipes = NULL;
 	}
-	if (dc->debug.disable_z10) {
-		/*hw not support z10 or sw disable it*/
-		dc->hwss.z10_restore = NULL;
-		dc->hwss.z10_save_init = NULL;
-	}
 }