[Intel-gfx] [PATCH i-g-t v2] tests: add slice power programming test

[Chris Wilson]

Quoting Lionel Landwerlin (2017-09-22 16:11:33)
> Verifies that the kernel programs slices correctly based by reading
> the value of PWR_CLK_STATE register.
> 
> v2: Add subslice tests (Lionel)
>     Use MI_SET_PREDICATE for further verification when available (Lionel)

Since this is being created from scratch, prefer the igt routines over
libdrm. We don't have to suffer the impedance mismatch in the
libdrm_intel interface...
-Chris