nvc0: add a new bin for the code segment

nvc0: add a new bin for the code segment

To avoid the bins list to grow up indefinitely when the code segment
size will be bumped, we need to separate that bin from the SCREEN
one because it contains other resources like the uniform bo.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>