drm/irq: Ditch DRIVER_IRQ_SHARED

This is only used by drm_irq_install(), which is an optional helper.
For legacy pci devices this is required (due to interrupt sharing without
msi/msi-x), and just making this the default exactly matches the behaviour
of all existing drivers using the drm_irq_install() helpers. In case that
ever becomes wrong drivers can roll their own irq handling, as many
drivers already do (for other reasons like needing a threaded interrupt
handler, or having an entire pile of different interrupt sources).

v2: Rebase

v3: Improve commit message (Emil)

Cc: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190129104248.26607-3-daniel.vetter@ffwll.ch

drivers/gpu/drm/i915/i915_drv.c

@@ -3209,7 +3209,7 @@ static struct drm_driver driver = {
 	 * deal with them for Intel hardware.
 	 */
 	.driver_features =
-	    DRIVER_IRQ_SHARED | DRIVER_GEM | DRIVER_PRIME |
+	    DRIVER_GEM | DRIVER_PRIME |
 	    DRIVER_RENDER | DRIVER_MODESET | DRIVER_ATOMIC | DRIVER_SYNCOBJ,
 	.release = i915_driver_release,
 	.open = i915_driver_open,