drm/irq: Don't check for DRIVER_HAVE_IRQ in drm_irq_(un)install

If a non-legacy driver calls these it's valid to assume there is
interrupt support. The flag is really only needed for legacy drivers,
which control IRQ enabling/disabling through the DRM_IOCTL_CONTROL
legacy IOCTL.

Also remove all the flag usage from non-legacy drivers.

v2: Review from Emil:
- improve commit message
- I forgot hibmc, fix that

Cc: linux-arm-kernel@lists.infradead.org
Cc: intel-gfx@lists.freedesktop.org
Cc: linux-amlogic@lists.infradead.org
Cc: linux-arm-msm@vger.kernel.org
Cc: freedreno@lists.freedesktop.org
Cc: virtualization@lists.linux-foundation.org
Cc: spice-devel@lists.freedesktop.org
Cc: amd-gfx@lists.freedesktop.org
Cc: linux-renesas-soc@vger.kernel.org
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190129104248.26607-1-daniel.vetter@ffwll.ch

drivers/gpu/drm/drm_irq.c

@@ -103,9 +103,6 @@ int drm_irq_install(struct drm_device *dev, int irq)
 	int ret;
 	unsigned long sh_flags = 0;
 
-	if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ))
-		return -EOPNOTSUPP;
-
 	if (irq == 0)
 		return -EINVAL;
 
@@ -174,9 +171,6 @@ int drm_irq_uninstall(struct drm_device *dev)
 	bool irq_enabled;
 	int i;
 
-	if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ))
-		return -EOPNOTSUPP;
-
 	irq_enabled = dev->irq_enabled;
 	dev->irq_enabled = false;