drm/i915: Remove duplicated irq_preinstall/uninstall hooks

All the irq_preinstall and irq_uninstall hooks are now identical. Let's
just rename them all the irq_reset and remove the pointless duplicates.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170818183705.27850-16-ville.syrjala@linux.intel.com