[Intel-gfx] [PATCH 3/3] drm/atomic-helper: Don't call atomic_update_plane when it stays off

[shuang.he at intel.com]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 6176
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                 -5              276/276              271/276
ILK                                  301/301              301/301
SNB                 -1              316/316              315/316
IVB                                  328/328              328/328
BYT                                  285/285              285/285
HSW                                  394/394              394/394
BDW                                  321/321              321/321
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
 PNV  igt at gem_userptr_blits@coherency-sync      CRASH(1)PASS(3)      CRASH(2)
 PNV  igt at gen3_render_linear_blits      FAIL(3)PASS(3)      FAIL(2)
 PNV  igt at gen3_render_mixed_blits      FAIL(2)PASS(3)      FAIL(2)
 PNV  igt at gen3_render_tiledx_blits      FAIL(3)PASS(3)      FAIL(2)
 PNV  igt at gen3_render_tiledy_blits      FAIL(3)PASS(3)      FAIL(2)
 SNB  igt at kms_flip@modeset-vs-vblank-race      DMESG_WARN(1)PASS(4)      DMESG_WARN(2)
(dmesg patch applied)drm:intel_dp_start_link_train[i915]]*ERROR*too_many_voltage_retries,give_up at too many voltage .* give up
drm:intel_dp_complete_link_train[i915]]*ERROR*failed_to_train_DP,aborting at failed to train .* aborting
drm:intel_dp_start_link_train[i915]]*ERROR*failed_to_get_link_status at failed to get link status
drm:intel_dp_complete_link_train[i915]]*ERROR*failed_to_start_channel_equalization at failed to start channel equalization
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