vc4: Reports nonzero OQ bits

[anholt]

gallium doesn't give the driver control of this, unfortunately. piglit tests fail, and apps don't get a chance to make correct choices.

[anholt]

Steps here:

• Add a new PIPE_CAP define for querying the number of OQ bits available. Update all existing drivers to say "64" (same as before) but i915 and vc4 to say "0"
• make state_tracker query the PIPE_CAP and set QueryCounterBits.SamplesPassed
• Go through piglit tests and make any that use SAMPLES_PASSED results check that the number of bits is not 0.