i965: Disable ARB_pipeline_statistics_query on Gen4-5.

i965: Disable ARB_pipeline_statistics_query on Gen4-5.

We apparently enabled this on all platforms in Mesa 10.6.  However, it
was only ever implemented for Gen6+.  The Gen4-5 query code goes up in
flames with an "Unrecognized query target" unreachable() error if you
even attempt to use any of the new functionality.

This wasn't caught because the Piglit tests require OpenGL 3.0, which
Gen4-5 cannot support.  The extension spec does say 3.0 is required,
though I'm not sure why - it seems like 2.1 would work fine.

We could implement it anyway, but it's a little bit of a pain due to the
lack of hardware contexts (so we have to snapshot around batches).

Given that it's been 100% broken for two years and I haven't seen a bug
report about it, I'm not terribly inclined to care.  So, let it go.

Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>