[Intel-gfx] [PATCH v3] drm/i915: Enable WaProgramMgsrForCorrectSliceSpecificMmioReads for Gen9

[Chiou, Cooper]

I've tested on GLK, KBL, CFL Intel NUC devices and got the following performance results, there is no performance regression per my testing.

Patch: [v5] drm/i915: Enable WaProgramMgsrForCorrectSliceSpecificMmioReads for Gen9
Test suite: phoronix-test-suite.supertuxkart.1024x768.Fullscreen.Ultimate.1.GranParadisoIsland.frames_per_second
Kernel version: 5.12.0-rc1 (drm-tip)

a. Device: Intel NUC kit NUC7JY Gemini Lake Celeron J4005 @2.7GHz (2 Cores)
    Without patch, fps=57.45
    With patch, fps=57.49
b. Device: Intel NUC kit NUC8BEH Coffee Lake Core i3-8109U @3.6GHz(4 Cores)
    Without patch, fps=117.23
    With patch, fps=117.27
c. Device: Intel NUC kit NUC7i3BNH Kaby Lake Core i3-7100U @2.4GHz(4 Cores)
    Without patch, fps=114.05
    With patch, fps=114.34

Meanwhile, Intel lkp team has validated performance on lkp-kbl-nuc1 and no regression.
f69d02e37a85645a  d912096c40cdc3bc9364966971 testcase/testparams/testbox
----------------  -------------------------- ---------------------------
          %stddev      change         %stddev
              \          |                \
      29.79                       29.67
phoronix-test-suite/performance-true-Fullscreen-Ultimate-1-Gran_Paradiso_Island__Approxima-supertuxkart-1.5.2-ucode=0xde/lkp-kbl-nuc1
      29.79                       29.67        GEO-MEAN phoronix-test-suite.supertuxkart.1280x1024.Fullscreen.Ultimate.1.GranParadisoIsland.frames_per_second

Best Regards,
Cooper

> We need testing on more that one box I'm afraid. Need to cover different
> fusing configs of Gen9 with and without the patch. I don't have any useful
> ideas on how to do it though. :(
> 
> Regards,
> 
> Tvrtko