drm/i915: expose rcs topology through query uAPI

With the introduction of asymmetric slices in CNL, we cannot rely on
the previous SUBSLICE_MASK getparam to tell userspace what subslices
are available. Here we introduce a more detailed way of querying the
Gen's GPU topology that doesn't aggregate numbers.

This is essential for monitoring parts of the GPU with the OA unit,
because counters need to be normalized to the number of
EUs/subslices/slices. The current aggregated numbers like EU_TOTAL do
not gives us sufficient information.

The Mesa series making use of this API is :

    https://patchwork.freedesktop.org/series/38795/

As a bonus we can draw representations of the GPU :

    https://imgur.com/a/vuqpa



v2: Rename uapi struct s/_mask/_info/ (Tvrtko)
    Report max_slice/subslice/eus_per_subslice rather than strides (Tvrtko)
    Add uapi macros to read data from *_info structs (Tvrtko)

v3: Use !!(v & DRM_I915_BIT()) for uapi macros instead of custom shifts (Tvrtko)

v4: factorize query item writting (Tvrtko)
    tweak uapi struct/define names (Tvrtko)

v5: Replace ALIGN() macro (Chris)

v6: Updated uapi comments (Tvrtko)
    Moved flags != 0 checks into vfuncs (Tvrtko)

v7: Use access_ok() before copying anything, to avoid overflows (Chris)
    Switch BUG_ON() to GEM_WARN_ON() (Tvrtko)

v8: Tweak uapi comments style to match the coding style (Lionel)

v9: Fix error in comment about computation of enabled subslice (Tvrtko)

v10: Fix/update comments in uAPI (Sagar)

v11: Drop drm_i915_query_(slice|subslice|eu)_info in favor of a single
     drm_i915_query_topology_info (Joonas)

v12: Add subslice_stride/eu_stride in drm_i915_query_topology_info (Joonas)

v13: Fix comment in uAPI (Joonas)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180306122857.27317-7-lionel.g.landwerlin@intel.com