[Intel-gfx] [PATCH] drm/i915: Exit early from psr_status if PSR is not supported by the device

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 5918
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  282/282              282/282
ILK                                  308/308              308/308
SNB                                  307/307              307/307
IVB                                  375/375              375/375
BYT                                  294/294              294/294
HSW                 -1              385/385              384/385
BDW                                  315/315              315/315
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*HSW  igt_gem_storedw_loop_blt      PASS(2)      DMESG_WARN(1)PASS(1)
Note: You need to pay more attention to line start with '*'