sfc: Create multiple TX queues

Create a core TX queue and 2 hardware TX queues for each channel.
If separate_tx_channels is set, create equal numbers of RX and TX
channels instead.

Rewrite the channel and queue iteration macros accordingly.
Eliminate efx_channel::used_flags as redundant.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/sfc/selftest.h

@@ -18,8 +18,8 @@
  */
 
 struct efx_loopback_self_tests {
-	int tx_sent[EFX_TX_QUEUE_COUNT];
-	int tx_done[EFX_TX_QUEUE_COUNT];
+	int tx_sent[EFX_TXQ_TYPES];
+	int tx_done[EFX_TXQ_TYPES];
 	int rx_good;
 	int rx_bad;
 };