i965: Add debug to INTEL_DEBUG=blorp describing hiz/blit/clear ops.

i965: Add debug to INTEL_DEBUG=blorp describing hiz/blit/clear ops.

I think we've all added instrumentation at one point or another to see
what's being called in blorp.  Now you can quickly get output like:

Testing glCopyPixels(depth).
intel_hiz_exec depth clear to mt 0x16d9160 level 0 layer 0
intel_hiz_exec depth resolve to mt 0x16d9160 level 0 layer 0
intel_hiz_exec hiz ambiguate to mt 0x16d9160 level 0 layer 0
intel_hiz_exec depth resolve to mt 0x16d9160 level 0 layer 0

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>