drm/i915: Do not call drm_crtc_arm_vblank_event in async flips

Since the flip done event will be sent in the flip_done_handler,
no need to add the event to the list and delay it for later.

v2: -Moved the async check above vblank_get as it
     was causing issues for PSR.

v3: -No need to wait for vblank to pass, as this wait was causing a
     16ms delay once every few flips.

v4: -Rebased.

v5: -Rebased.

v6: -Rebased.

v7: -No need of irq disable if we are not doing vblank evade. (Ville)

v8: -Rebased.

v9: -Move the return in intel_pipe_update_end before tracepoint. (Ville)

v10: Rebased.

Signed-off-by: Karthik B S <karthik.b.s@intel.com>
Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200921110210.21182-5-karthik.b.s@intel.com