net: ethernet: ti am65_cpsw: Drop separate TX completion functions

Drop separate TX completion functions for SKB and XDP. To do that
use the SW_DATA mechanism to store ndev and skb/xdpf for TX packets.

Use BUILD_BUG_ON_MSG() to fail build if SW_DATA size exceeds whats
available. i.e. AM65_CPSW_NAV_SW_DATA_SIZE.

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>