gianfar: Use pr_<level>, netdev_<level> and netif_<level>

Use the current logging styles.

Add #define DEBUG to get same output for <foo>_dbg messages.
Convert a few bare printks to pr_err.

Fix a likely copy/paste defect where a test was done with RX values:
        if (num_rx_qs > MAX_RX_QS) {
but TX limits were emitted:
        printk(KERN_ERR "num_rx_qs(=%d) greater than MAX_RX_QS(=%d)\n",
                              num_tx_qs, MAX_TX_QS);

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@conan.davemloft.net>