drm/i915/cnl: Add support slice/subslice/eu configs

drm/i915/cnl: Add support slice/subslice/eu configs

Cannonlake Slice and Subslice information has changed.

This patch initially provided by Ben adds the proper sseu
initialization.

v2: This v2 done by Rodrigo includes:
    - Fix on Total slices count by avoiding [1][2] and [2][2].
    - Inclusion of EU Per Subslice.
    - Commit message.
v3: This v3 done by Rodrigo includes:
    - Handle all possible bits and extra fuse register.
    - Use INTEL_GEN macro.
    - Fully assume uniform distribution so remove union
      with eu_per_subslice and add proper the comment.
v4: This v4 done by Rodrigo includes:
    - Consider all bits available: 6 bits for slices [27:22]
      and 4 for subslices [21:18].
v5: This v5 done by Rodrigo includes:
    - sseu->subslice_mask = (1 << 4) - 1 - missed on previous
    versions and noticed by Oscar.

Cc: Oscar Mateo <oscar.mateo@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Oscar Mateo <oscar.mateo@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170920183525.20530-1-rodrigo.vivi@intel.com