amdgpu/gmc_v9: save/restore sdpif regs during S3

fixes S3 issue with IOMMU + S/G  enabled @ 64M VRAM.

Suggested-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h
index d3c27a3..7546da0 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gmc.h
@@ -195,6 +195,7 @@ struct amdgpu_gmc {
 	uint32_t                srbm_soft_reset;
 	bool			prt_warning;
 	uint64_t		stolen_size;
+	uint32_t		sdpif_register;
 	/* apertures */
 	u64			shared_aperture_start;
 	u64			shared_aperture_end;