drm/amdgpu: Convert to using devm_drm_dev_alloc() (v2)

Convert to using devm_drm_dev_alloc(),
as drm_dev_init() is going away.

v2: Remove drm_dev_put() since
    a) devres doesn't do refcounting, see
    Documentation/driver-api/driver-model/devres.rst,
    Section 4, paragraph 1; and since
    b) devres acts as garbage collector when
    the DRM device's parent's devres "action" callback
    is called to free the container device (amdgpu_device),
    which embeds the DRM dev.

Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200918132505.2316382-4-daniel.vetter@ffwll.ch

Author: Luben Tuikov

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

@@ -1142,25 +1142,20 @@ static int amdgpu_pci_probe(struct pci_dev *pdev,
 	if (ret)
 		return ret;
 
-	adev = kzalloc(sizeof(*adev), GFP_KERNEL);
-	if (!adev)
-		return -ENOMEM;
+	adev = devm_drm_dev_alloc(&pdev->dev, &kms_driver, typeof(*adev), ddev);
+	if (IS_ERR(adev))
+		return PTR_ERR(adev);
 
 	adev->dev  = &pdev->dev;
 	adev->pdev = pdev;
 	ddev = adev_to_drm(adev);
-	ret = drm_dev_init(ddev, &kms_driver, &pdev->dev);
-	if (ret)
-		goto err_free;
-
-	drmm_add_final_kfree(ddev, adev);
 
 	if (!supports_atomic)
 		ddev->driver_features &= ~DRIVER_ATOMIC;
 
 	ret = pci_enable_device(pdev);
 	if (ret)
-		goto err_free;
+		return ret;
 
 	ddev->pdev = pdev;
 	pci_set_drvdata(pdev, ddev);
@@ -1188,8 +1183,6 @@ static int amdgpu_pci_probe(struct pci_dev *pdev,
 
 err_pci:
 	pci_disable_device(pdev);
-err_free:
-	drm_dev_put(ddev);
 	return ret;
 }
 
@@ -1206,7 +1199,6 @@ amdgpu_pci_remove(struct pci_dev *pdev)
 	amdgpu_driver_unload_kms(dev);
 	pci_disable_device(pdev);
 	pci_set_drvdata(pdev, NULL);
-	drm_dev_put(dev);
 }
 
 static void