[lan78xx] Always enable automatic speed and duplex detection

On devices with no EEPROM or OTP, the MAC_CR register defaults to not
using automatic link speed detection, with the result that no packets
are successfully sent or received.

Fix by always enabling automatic speed and duplex detection, since
iPXE provides no mechanism for manual configuration of either link
speed or duplex.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/lan78xx.c

 				     LAN78XX_BULK_IN_DLY_SET ( 0 ) ) ) != 0 )
 		goto err_bulk_in_dly;
 
+	/* Enable automatic speed and duplex detection */
+	if ( ( rc = smscusb_writel ( smscusb, LAN78XX_MAC_CR,
+				     ( LAN78XX_MAC_CR_ADP |
+				       LAN78XX_MAC_CR_ADD |
+				       LAN78XX_MAC_CR_ASD ) ) ) != 0 )
+		goto err_mac_cr;
+
 	/* Configure receive filters */
 	if ( ( rc = smscusb_writel ( smscusb, LAN78XX_RFE_CTL,
 				     ( LAN78XX_RFE_CTL_AB |
  err_fct_tx_ctl:
  err_fct_rx_ctl:
  err_rfe_ctl:
+ err_mac_cr:
  err_bulk_in_dly:
  err_int_ep_ctl:
 	usbnet_close ( &smscusb->usbnet );

src/drivers/net/lan78xx.h

 #define LAN78XX_FCT_TX_CTL 0x00c4
 #define LAN78XX_FCT_TX_CTL_EN		0x80000000UL	/**< FCT TX enable */
 
+/** MAC control register */
+#define LAN78XX_MAC_CR 0x0100
+#define LAN78XX_MAC_CR_ADP		0x00002000UL	/**< Duplex polarity */
+#define LAN78XX_MAC_CR_ADD		0x00001000UL	/**< Auto duplex */
+#define LAN78XX_MAC_CR_ASD		0x00000800UL	/**< Auto speed */
+
 /** MAC receive register */
 #define LAN78XX_MAC_RX 0x0104
 #define LAN78XX_MAC_RX_MAX_SIZE(mtu)	( (mtu) << 16 )	/**< Max frame size */