!UPSTREAM: i965/gen7+: Implement fast color clear operation in blorp.

I've verified that this blorp program puts the right data in the MCS
buffer.

TODO:

- When doing a fast color clear, flag the surface as needing a fast
  color resolve.

- Create a field in intel_mipmap_tree to store clear color bits.

- When configuring SURFACE_STATE, copy clear color bits from
  intel_mipmap_tree.

- In brw_blorp_clear_params constructor, if doing a fast clear, store
  appropriate bits in intel_mipmap_tree to represent the clear color.

- Support more than just (0.0, 0.0, 0.0, 0.0) in
  is_color_fast_clear_compatible().
!UPSTREAM: Temporary debugging hack to print out contents of MCS buffer
!UPSTREAM: i965/blorp: Expand clear class hierarchy to prepare for RT resolves.

The fragment shaders that to do color clears will be re-used to
perform so-called "render target resolves" (the resolves associated
with fast color clears).  To prepare for that, this patch expands the
class hierarchy for blorp params: brw_blorp_clear_params (which will
be used for both fast and slow color clears) derives from
brw_blorp_const_color_params (which will be used for all blorp
operations where the fragment shader outputs a constant color).

Some other data structures and functions were also renamed to use
"const_color" nomenclature where appropriate.

TODO: Move earlier in series.
!UPSTREAM: i965/blorp: Write blorp code to do color resolves.

TODO:

- Test that this actually works.