!UPSTREAM: i965/gen7+: Allocate MCS buffers for use by fast color clears.

TODO:

- write blorp code to do fast color clears

- write blorp code to do color resolves

- write code to ensure that color resolves happen when necessary

- write code to do fast rather than slow color clears when possible

- Create a bit to keep track of whether a resolve is necessary

- Figure out an appropriate initial state for the buffer and the
  "needs resolve" bit.
!UPSTREAM: WIP

TODO:

- Support integers in is_color_fast_clear_compatible() (or maybe it's
  easier to just bail on integer fast clears).

- Test that the new blorp program puts the right data in the MCS
  buffer.

- 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().