net: Move driver-model code into its own file

Every other uclass is in its own file. Create a new eth-uclass.c file and
move the driver-model code into it, so that networking is consistent.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/net/Makefile b/net/Makefile
index b3a22c2..943de14 100644
--- a/net/Makefile
+++ b/net/Makefile
@@ -12,7 +12,11 @@
 obj-$(CONFIG_CMD_NET)  += bootp.o
 obj-$(CONFIG_CMD_CDP)  += cdp.o
 obj-$(CONFIG_CMD_DNS)  += dns.o
+ifdef CONFIG_DM_ETH
+obj-$(CONFIG_CMD_NET)  += eth-uclass.o
+else
 obj-$(CONFIG_CMD_NET)  += eth.o
+endif
 obj-$(CONFIG_CMD_NET)  += eth_common.o
 obj-$(CONFIG_CMD_LINK_LOCAL) += link_local.o
 obj-$(CONFIG_CMD_NET)  += net.o