drm/amdgpu/gmc11: 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

Fixes: 67318cb8 ("drm/amdgpu/gmc11: set gart placement GC11")
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_v11_0.c

@@ -642,7 +642,7 @@ static void gmc_v11_0_vram_gtt_location(struct amdgpu_device *adev,
 	amdgpu_gmc_gart_location(adev, mc, AMDGPU_GART_PLACEMENT_HIGH);
 	if (!amdgpu_sriov_vf(adev) &&
 	    (amdgpu_ip_version(adev, GC_HWIP, 0) < IP_VERSION(11, 5, 0)) &&
-	    (amdgpu_agp != 0))
+	    (amdgpu_agp == 1))
 		amdgpu_gmc_agp_location(adev, mc);
 
 	/* base offset of vram pages */