i965/fs: Pass current execution size to brw_IF() and brw_DO().

i965/fs: Pass current execution size to brw_IF() and brw_DO().

This gets IF and DO instructions working in SIMD32 programs.  brw_IF()
and brw_DO() should probably behave in the same way as other generator
functions that emit control flow instructions and just figure out the
right execution size by themselves from the current execution controls
specified through the brw_codegen argument.  Changing that will
require updating lots of Gen4-5 clipper code though, so for the moment
just pass the current value redundantly from the FS generator.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>