i965: Rework 3DSTATE_VS for Broadwell.

i965: Rework 3DSTATE_VS for Broadwell.

v2: Remove incorrect MOCS shifts; rename urb_entry_write_offset to
    urb_entry_output_offset to closer match the documentation.

v3: Only emit a non-zero constant buffer read length when active.

v4: Add missing binding table counts (caught by Eric).

v5: Rebase on Paul Berry's changes to CurrentVertexProgram.

v6: Drop bogus SBE read length/offset field code.  We were programming
    the wrong values, and our 3DSTATE_SBE code overrides any value we
    put here anyway with the correct one.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net> [v4]