i965: Add new SIMD8 VS prog data flag

i965: Add new SIMD8 VS prog data flag

This flag signals that we have a SIMD8 VS shader so we can set up the
corresponding state accordingly.  This boils down to setting
the BDW+ SIMD8 enable bit in 3DSTATE_VS and making UBO and pull
constant buffers use dword pitch.

Signed-off-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>