Revert "drm/amd/amdgpu: set gtt size according to system memory size only"

This reverts commit ba851eed895c76be0eb4260bdbeb7e26f9ccfaa2.
With that change piglit max size tests (running with -t max.*size) are causing
OOM and hard hang on my CZ with 1GB RAM.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Roger He <Hongbo.He@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1424,9 +1424,11 @@ int amdgpu_ttm_init(struct amdgpu_device *adev)
 		struct sysinfo si;
 
 		si_meminfo(&si);
-		gtt_size = max(AMDGPU_DEFAULT_GTT_SIZE_MB << 20,
-			(uint64_t)si.totalram * si.mem_unit * 3/4);
-	} else
+		gtt_size = min(max((AMDGPU_DEFAULT_GTT_SIZE_MB << 20),
+			       adev->mc.mc_vram_size),
+			       ((uint64_t)si.totalram * si.mem_unit * 3/4));
+	}
+	else
 		gtt_size = (uint64_t)amdgpu_gtt_size << 20;
 	r = ttm_bo_init_mm(&adev->mman.bdev, TTM_PL_TT, gtt_size >> PAGE_SHIFT);
 	if (r) {