i965/gs: Use NIR info for setting up prog_data

i965/gs: Use NIR info for setting up prog_data

Previously, we were pulling bits from GL data structures in order to set up
the prog_data.  However, in this brave new world of NIR, we want to be
pulling it out of the NIR shader whenever possible.  This way, we can move
all this setup code into brw_compile_gs without depending on the old GL
stuff.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>