net: lwip: add DHCP support and dhcp commmand

Add what it takes to enable NETDEVICES with NET_LWIP and enable DHCP as
well as the dhcp command. CMD_TFTPBOOT is selected by BOOTMETH_EFI due
to this code having an implicit dependency on do_tftpb().

Note that PXE is likely non-fonctional with NET_LWIP (or at least not
100% functional) because DHCP option 209 is not supported by the lwIP
library. Therefore, BOOTP_PXE_DHCP_OPTION cannot be enabled.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/board/xilinx/common/board.c b/board/xilinx/common/board.c
index 68f401e..38dd805 100644
--- a/board/xilinx/common/board.c
+++ b/board/xilinx/common/board.c
@@ -491,7 +491,8 @@
 				ret |= env_set_by_index("uuid", id, uuid);
 			}
 
-			if (!CONFIG_IS_ENABLED(NET))
+			if (!(CONFIG_IS_ENABLED(NET) ||
+			      CONFIG_IS_ENABLED(NET_LWIP)))
 				continue;
 
 			for (i = 0; i < EEPROM_HDR_NO_OF_MAC_ADDR; i++) {