drm/amdgpu/gmc10: disable AGP aperture

We've had misc reports of random IOMMU page faults when
this is used.  It's just a rarely used optimization anyway, so
let's just disable it.  It can still be toggled via the
module parameter for testing.

v2: leave it configurable via module parameter

Reviewed-by: Yang Wang <kevinyang.wang@amd.com> (v1)
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Tested-by: Mario Limonciello <mario.limonciello@amd.com> # PHX & Navi33
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gmc_v10_0.c

@@ -675,7 +675,7 @@ static void gmc_v10_0_vram_gtt_location(struct amdgpu_device *adev,
 	amdgpu_gmc_set_agp_default(adev, mc);
 	amdgpu_gmc_vram_location(adev, &adev->gmc, base);
 	amdgpu_gmc_gart_location(adev, mc, AMDGPU_GART_PLACEMENT_BEST_FIT);
-	if (!amdgpu_sriov_vf(adev) && (amdgpu_agp != 0))
+	if (!amdgpu_sriov_vf(adev) && (amdgpu_agp == 1))
 		amdgpu_gmc_agp_location(adev, mc);
 
 	/* base offset of vram pages */