drm/i915/guc: move guc irq functions to intel_guc parameter

No functional change, just moving the guc_to_i915 from the caller into
the irq function. This will help with the upcoming move of guc under
intel_gt.

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190713100016.8026-4-chris@chris-wilson.co.uk
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>