i965/fs: Show register pressure in dump_instructions() output.

i965/fs: Show register pressure in dump_instructions() output.

Dumping the number of live registers at each IP allows us to see
register pressure and identify any local maxima.  This should
aid in debugging passes designed to reduce register pressure, as
well as optimizations that suddenly trigger spilling.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>