sync up t_vp_build.c brw_vs_tnl.c a bit

sync up t_vp_build.c brw_vs_tnl.c a bit

Bring over the optimizations for fog and normalized spot dir
from t_vp_build.c to brw_vs_tnl.c. Likewise, port a fix for point size
calc from brw_vs_tnl.c to t_vp_build.c (use ABS(eyez) instead of -eyez). Leave
the now differing point size calcs alone though, not sure what's better (it's
basically MOV, ABS, MUL, DP3 vs. ABS, MAD, MAD).