i965: old VS: use the VUE map to compute the URB entry size.

i965: old VS: use the VUE map to compute the URB entry size.

Previously, the old VS backend computed the URB entry size by adding
the number of vertex shader outputs to the size of the URB header.
This often produced a larger result than necessary, because some
vertex shader outputs are stored in the header, so they were being
double counted.  This patch changes the old VS backend to compute the
URB entry size directly from the number of slots in the VUE map.

Note: there's a subtle change in that we no longer count header
registers towards the size of the VF input.  I believe this is
correct, because the header is only emitted in the output of the VS
stage--it is not present in the input.  (As evidence for this, note
that brw_vs_state.c sets urb_entry_read_offset to 0--it does not
include space for the header as part of the VS input).

Reviewed-by: Eric Anholt <eric@anholt.net>