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/net/Makefile b/net/Makefile
index 34fe501..209377a 100644
--- a/net/Makefile
+++ b/net/Makefile
@@ -12,11 +12,6 @@
 obj-$(CONFIG_CMD_CDP)  += cdp.o
 obj-$(CONFIG_CMD_DNS)  += dns.o
 obj-$(CONFIG_DM_DSA)   += dsa-uclass.o
-obj-$(CONFIG_$(XPL_)DM_ETH) += eth-uclass.o
-obj-$(CONFIG_$(PHASE_)BOOTDEV_ETH) += eth_bootdev.o
-obj-$(CONFIG_DM_MDIO)  += mdio-uclass.o
-obj-$(CONFIG_DM_MDIO_MUX) += mdio-mux-uclass.o
-obj-$(CONFIG_$(XPL_)DM_ETH) += eth_common.o
 obj-$(CONFIG_CMD_LINK_LOCAL) += link_local.o
 obj-$(CONFIG_IPV6)     += ndisc.o
 obj-$(CONFIG_$(XPL_)DM_ETH) += net.o
@@ -43,4 +38,13 @@
 
 endif
 
+ifeq ($(filter y,$(CONFIG_NET) $(CONFIG_NET_LWIP)),y)
+obj-$(CONFIG_$(XPL_)DM_ETH) += eth-uclass.o
+obj-$(CONFIG_$(PHASE_)BOOTDEV_ETH) += eth_bootdev.o
+obj-$(CONFIG_DM_MDIO)  += mdio-uclass.o
+obj-$(CONFIG_DM_MDIO_MUX) += mdio-mux-uclass.o
+obj-$(CONFIG_$(XPL_)DM_ETH) += eth_common.o
 obj-y += net-common.o
+endif
+
+obj-$(CONFIG_NET_LWIP) += lwip/