drm/amd/display: Add skip rIOMMU dc config option

[Why]
Need option to skip rIOMMU calls for dcn21.

[How]
Added rIOMMU dc config option and check for whether to skip
rIOMMU calls.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Kevin Gao <kgao1003@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Kevin Gao

drivers/gpu/drm/amd/display/dc/dc.h

@@ -448,6 +448,7 @@ struct dc_config {
 	bool enable_windowed_mpo_odm;
 	bool forceHBR2CP2520; // Used for switching between test patterns TPS4 and CP2520
 	uint32_t allow_edp_hotplug_detection;
+	bool skip_riommu_prefetch_wa;
 	bool clamp_min_dcfclk;
 	uint64_t vblank_alignment_dto_params;
 	uint8_t  vblank_alignment_max_frame_time_diff;

drivers/gpu/drm/amd/display/dc/hubbub/dcn21/dcn21_hubbub.c

@@ -132,9 +132,9 @@ int hubbub21_init_dchub(struct hubbub *hubbub,
 		// Init VMID 0 based on PA config
 		dcn20_vmid_setup(&hubbub1->vmid[0], &phys_config);
 	}
-
-	dcn21_dchvm_init(hubbub);
-
+	if (!hubbub1->base.ctx->dc->config.skip_riommu_prefetch_wa) {
+		dcn21_dchvm_init(hubbub);
+	}
 	return hubbub1->num_vmid;
 }