i965/fs: Do instruction pre-scheduling just before register allocation.

i965/fs: Do instruction pre-scheduling just before register allocation.

Long ago, the HW_REG usage in assign_curb/urb_setup() were scheduling
barriers, so we had to run scheduler before them in order for it to be
able to do basically anything.  Now that that's fixed, we can delay the
scheduling until we go to allocate (which will make the next change less
scary).

Cc: "10.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>