drm/msm: split the main platform driver

Currently the msm platform driver is a multiplex handling several cases:
- headless GPU-only driver,
- MDP4 with flat device nodes,
- MDP5/DPU MDSS with all the nodes being children of MDSS node.

This results in not-so-perfect code, checking the hardware version
(MDP4/MDP5/DPU) in several places, checking for mdss even when it can
not exist, etc. Split the code into three handling subdrivers (mdp4,
mdss and headless msm).

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/482507/
Link: https://lore.kernel.org/r/20220419155346.1272627-4-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/disp/mdp4/mdp4_kms.c

@@ -569,3 +569,59 @@ static struct mdp4_platform_config *mdp4_get_config(struct platform_device *dev)
 
 	return &config;
 }
+
+static const struct dev_pm_ops mdp4_pm_ops = {
+	.prepare = msm_pm_prepare,
+	.complete = msm_pm_complete,
+};
+
+static int mdp4_probe(struct platform_device *pdev)
+{
+	struct msm_drm_private *priv;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, priv);
+
+	/*
+	 * on MDP4 based platforms, the MDP platform device is the component
+	 * that adds other display interface components to itself.
+	 */
+	return msm_drv_probe(&pdev->dev, &pdev->dev);
+}
+
+static int mdp4_remove(struct platform_device *pdev)
+{
+	component_master_del(&pdev->dev, &msm_drm_ops);
+
+	return 0;
+}
+
+static const struct of_device_id mdp4_dt_match[] = {
+	{ .compatible = "qcom,mdp4", .data = (void *)KMS_MDP4 },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, mdp4_dt_match);
+
+static struct platform_driver mdp4_platform_driver = {
+	.probe      = mdp4_probe,
+	.remove     = mdp4_remove,
+	.shutdown   = msm_drv_shutdown,
+	.driver     = {
+		.name   = "mdp4",
+		.of_match_table = mdp4_dt_match,
+		.pm     = &mdp4_pm_ops,
+	},
+};
+
+void __init msm_mdp4_register(void)
+{
+	platform_driver_register(&mdp4_platform_driver);
+}
+
+void __exit msm_mdp4_unregister(void)
+{
+	platform_driver_unregister(&mdp4_platform_driver);
+}