i965: Add support for xfb overflow query on conditional render.

i965: Add support for xfb overflow query on conditional render.

Enable the use of a transform feedback overflow query with
glBeginConditionalRender. The render commands will only execute if the
query is true (i.e. if there was an overflow).

Use ARB_conditional_render_inverted to change this behavior.

v4:
    - reuse MI_MATH calcs from hsw_queryob (Kenneth)
    - fallback to software conditional rendering when MI_MATH is not
      available (Kenneth)

v5:
    - check query->Target (Kenneth)

Signed-off-by: Rafael Antognolli <rafael.antognolli@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>