drm: Nuke ums vgaarb support

i915, nouveau (ever since merged to upstream) and radeon all lack ums
support in upstream. No point keeping the ums vgaarb support around.
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170125062657.19270-12-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_irq.c

@@ -415,29 +415,6 @@ int drm_vblank_init(struct drm_device *dev, unsigned int num_crtcs)
 }
 EXPORT_SYMBOL(drm_vblank_init);
 
-static void drm_irq_vgaarb_nokms(void *cookie, bool state)
-{
-	struct drm_device *dev = cookie;
-
-	if (dev->driver->vgaarb_irq) {
-		dev->driver->vgaarb_irq(dev, state);
-		return;
-	}
-
-	if (!dev->irq_enabled)
-		return;
-
-	if (state) {
-		if (dev->driver->irq_uninstall)
-			dev->driver->irq_uninstall(dev);
-	} else {
-		if (dev->driver->irq_preinstall)
-			dev->driver->irq_preinstall(dev);
-		if (dev->driver->irq_postinstall)
-			dev->driver->irq_postinstall(dev);
-	}
-}
-
 /**
  * drm_irq_install - install IRQ handler
  * @dev: DRM device
@@ -492,9 +469,6 @@ int drm_irq_install(struct drm_device *dev, int irq)
 		return ret;
 	}
 
-	if (drm_core_check_feature(dev, DRIVER_LEGACY))
-		vga_client_register(dev->pdev, (void *)dev, drm_irq_vgaarb_nokms, NULL);
-
 	/* After installing handler */
 	if (dev->driver->irq_postinstall)
 		ret = dev->driver->irq_postinstall(dev);

include/drm/drm_drv.h

@@ -345,9 +345,6 @@ struct drm_driver {
 	int (*gem_prime_mmap)(struct drm_gem_object *obj,
 				struct vm_area_struct *vma);
 
-	/* vga arb irq handler */
-	void (*vgaarb_irq)(struct drm_device *dev, bool state);
-
 	/**
 	 * @dumb_create:
 	 *