i965: Add support for GL_AMD_performance_monitor on Ironlake.

i965: Add support for GL_AMD_performance_monitor on Ironlake.

Ironlake's counters are always enabled; userspace can simply send a
MI_REPORT_PERF_COUNT packet to take a snapshot of them.  This makes it
easy to implement.

The counters are documented in the source code for the intel-gpu-tools
intel_perf_counters utility.

v2: Adjust for core data structure changes.  Add a table mapping buffer
    object offsets to exposed counters (which changes each generation).
    Finally, add report ID assertions to sanity check the BO layout
    (thanks to Carl Worth).

v3: Update for core BeginPerfMonitor hook changes (requested by Brian).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>