drm/i915: Rename GEN8_PIPE_FLIP_DONE to PRIMARY_FLIP_DONE

It is now clear that this interrupt is for the primary plane and not
something global to the pipe. It also matches what the spec calls it.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/i915_irq.c
Simple merge

diff --cc drivers/gpu/drm/i915/i915_reg.h
Simple merge