i965 new VS: Fix bugs in pre-GEN6 psiz/flags computation

i965 new VS: Fix bugs in pre-GEN6 psiz/flags computation

This patch corrects two errors in the computation of the psiz/flags
VUE slot on pre-GEN5 when using the new VS backend:

- The clip flags (which should be stored in the w component of the
  first VUE slot) were being accidentally duplicated in all other
  components of that VUE slot, causing partially clipped triangles to
  sometimes disappear completely.

- The OR instruction wasn't being stored in "inst", causing the
  BRW_PREDICATE_NORMAL flag to be applied to the wrong instruction.

This patch fixes regressions in clipping behavior when using shaders
on GEN4-5.

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