drm/i915: stop including i915_irq.h from i915_drv.h

Only include i915_irq.h where actually needed.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220105102131.988791-1-jani.nikula@intel.com