net: ethernet: ti: am65-cpsw: Re-arrange functions to avoid forward declaration

Re-arrange am65_cpsw_nuss_rx_cleanup(), am65_cpsw_nuss_xmit_free() and
am65_cpsw_nuss_tx_cleanup() to avoid forward declaration.

No functional change.

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>