drm/bridge/synopsys: dw-hdmi: Add an option to suppress loading CEC driver

This adds DW-HDMI driver a glue option to disable loading of the CEC sub-driver.

On some SoCs, the CEC functionality is enabled in the IP config bits, but the
CEC bus is non-functional like on Amlogic SoCs, where the CEC config bit is set
but the DW-HDMI CEC signal is not connected to a physical pin, leading to some
confusion when the DW-HDMI CEC controller can't communicate on the bus.
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Link: https://patchwork.freedesktop.org/patch/msgid/20210416092737.1971876-2-narmstrong@baylibre.com

drivers/gpu/drm/bridge/synopsys/dw-hdmi.c

@@ -3421,7 +3421,7 @@ struct dw_hdmi *dw_hdmi_probe(struct platform_device *pdev,
 		hdmi->audio = platform_device_register_full(&pdevinfo);
 	}
 
-	if (config0 & HDMI_CONFIG0_CEC) {
+	if (!plat_data->disable_cec && (config0 & HDMI_CONFIG0_CEC)) {
 		cec.hdmi = hdmi;
 		cec.ops = &dw_hdmi_cec_ops;
 		cec.irq = irq;

include/drm/bridge/dw_hdmi.h

@@ -153,6 +153,8 @@ struct dw_hdmi_plat_data {
 	const struct dw_hdmi_phy_config *phy_config;
 	int (*configure_phy)(struct dw_hdmi *hdmi, void *data,
 			     unsigned long mpixelclock);
+
+	unsigned int disable_cec : 1;
 };
 
 struct dw_hdmi *dw_hdmi_probe(struct platform_device *pdev,