drm/msm: add modeset module param

At least for debugging it is nice to have an easy way to force the
driver not to load.
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/msm_drv.c

@@ -73,6 +73,10 @@ bool dumpstate = false;
 MODULE_PARM_DESC(dumpstate, "Dump KMS state on errors");
 module_param(dumpstate, bool, 0600);
 
+static bool modeset = true;
+MODULE_PARM_DESC(modeset, "Use kernel modesetting [KMS] (1=on (default), 0=disable)");
+module_param(modeset, bool, 0600);
+
 /*
  * Util/helpers:
  */
@@ -1133,6 +1137,9 @@ static struct platform_driver msm_platform_driver = {
 
 static int __init msm_drm_register(void)
 {
+	if (!modeset)
+		return -EINVAL;
+
 	DBG("init");
 	msm_mdp_register();
 	msm_dsi_register();