drm: xlnx_mixer: Added module variable to enable/disable primary plane.

Enabling primary plan by default is causing bandwidth of 2GB
To overcome such issues, this varilable is introduced in module,
which can be enable or disable using below sysfs commands:

Enable:
echo Y > /sys/module/xlnx_mixer/parameters/mixer_primary_enable

Disable:
echo N > /sys/module/xlnx_mixer/parameters/mixer_primary_enable

Signed-off-by: Nayan Bhavsar <nayan.bhavsar@xilinx.com>

drivers/gpu/drm/xlnx/xlnx_mixer.c

@@ -240,6 +240,10 @@ static const u32 color_table[] = {
 	DRM_FORMAT_XV20,
 };
 
+static bool xlnx_mixer_primary_enable = true;
+module_param_named(mixer_primary_enable, xlnx_mixer_primary_enable, bool, 0600);
+MODULE_PARM_DESC(mixer_primary_enable, "Enable mixer primary plane (default: 1)");
+
 /*********************** Inline Functions/Macros *****************************/
 #define to_mixer_hw(p) (&((p)->mixer->mixer_hw))
 #define to_xlnx_crtc(x)	container_of(x, struct xlnx_crtc, crtc)
@@ -743,6 +747,13 @@ static void xlnx_mix_layer_enable(struct xlnx_mix_hw *mixer,
 {
 	struct xlnx_mix_layer_data *layer_data;
 	u32 curr_state;
+	struct xlnx_mix *mix;
+
+	mix = container_of(mixer, struct xlnx_mix, mixer_hw);
+	if (mix->drm_primary_layer->mixer_layer->id == id) {
+		if (!xlnx_mixer_primary_enable)
+			return;
+	}
 
 	/* Ensure layer is marked as 'active' by application before
 	 * turning on in hardware.  In some cases, layer register data