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

TODO:

- 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

- Do we need to do any extra work for window system color buffers?

- In circumstances where SwapBuffers() makes the back buffer contents
  undefined (when is this?), can we save time by doing a pre-emptive
  fast color clear?  (Seems like it would save time by avoiding
  unnecessary reads when rendering causes a cache miss) Note: a lot of
  apps probably do a glClear() as the first operation after a swap, so
  to avoid slowing down those apps, we probably would only want to do
  this if we also were able to detect redundant clears (see above).
!UPSTREAM: i965/gen7+: Support fast color clear values other than (0,0,0,0)

TODO:

- Test

- Move into earlier patches
!UPSTREAM: Temporary debugging hack to dump clear color bits
!UPSTREAM: Temporary debugging hack to print out contents of MCS buffer
!UPSTREAM: Temporary debugging hack to test RT resolves
!UPSTREAM: Stop doing pre-emptive resolves