add i965 primitive restart hardware support where possible v2: * Only enable NV_primitive_restart for gen >= 4 * Move function names to the beginning of lines * Don't include brw_context.h from brw_draw.h * brw_handle_primitive_restart returns GLboolean instead of bool * Only call vbo_sw_primitive_restart once in brw_handle_primitive_restart * Add comments to various functions v1: * Enable NV_primitive_restart for all hardware. (Software primitive restart is used where necessary) * If hardware supports cut index and cut index can handle the primitive restart scenario, then use cut index to implement hardware support for primitive restart during the draw.