[Intel-gfx] [PATCH] drm/i915: Don't clobber plane state on internal disables

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 5887
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  280/280              280/280
ILK                                  308/308              308/308
SNB                 -1              328/328              327/328
IVB                 -1              379/379              378/379
BYT                                  294/294              294/294
HSW                                  387/387              387/387
BDW                 -1              316/316              315/316
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
 SNB  igt_kms_rotation_crc_sprite-rotation      DMESG_WARN(1)PASS(4)      DMESG_WARN(2)
*IVB  igt_kms_rotation_crc_sprite-rotation      PASS(2)      DMESG_WARN(2)
*BDW  igt_gem_gtt_hog      PASS(3)      DMESG_WARN(1)PASS(1)
Note: You need to pay more attention to line start with '*'