mlxsw: spectrum: acl: Push code related to num_ctcam_erps inc/dec into separate helpers

Later on the same code is going to be needed for deltas as well. So push
the procedures related to increment and decrement of num_ctcam_erps
into a separate helpers.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>