i965: Use a line end cap width of 0.5 unless smooth lines enabled.

i965: Use a line end cap width of 0.5 unless smooth lines enabled.

This updates the Gen4-5 code to use a line end cap width of 0.5
for non-smooth lines, and 1.0 for smooth lines - which is what we
do on Gen6+.

Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>