[Intel-gfx] [PATCH] drm/i915: Preserve ddi_pll_sel when allocating new pipe_config

[shuang.he at intel.com]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 6415
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  276/276              276/276
ILK                                  283/283              283/283
SNB                 -1              314/314              313/314
IVB                                  338/338              338/338
BYT                                  286/286              286/286
BDW                                  320/320              320/320
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
 SNB  igt at pm_rpm@dpms-mode-unset-non-lpsp      DMESG_WARN(14)PASS(1)      DMESG_WARN(1)
(dmesg patch applied)WARNING:at_drivers/gpu/drm/i915/intel_uncore.c:#assert_device_not_suspended[i915]()@WARNING:.* at .* assert_device_not_suspended+0x
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