bootstd: ethernet: Add a bootdev driver

Add a bootdev driver for Ethernet. It can use the PXE boot mechanism to
locate a file, added later.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/net/Kconfig b/net/Kconfig
index ef0aa16..964a4fe 100644
--- a/net/Kconfig
+++ b/net/Kconfig
@@ -25,6 +25,15 @@
 	  Enable a generic udp framework that allows defining a custom
 	  handler for udp protocol.
 
+config BOOTDEV_ETH
+	bool "Enable bootdev for ethernet"
+	depends on BOOTSTD
+	default y
+	help
+	  Provide a bootdev for ethernet so that is it possible to boot
+	  an operationg system over the network, using the PXE (Preboot
+	  Execution Environment) protocol.
+
 config BOOTP_SEND_HOSTNAME
 	bool "Send hostname to DNS server"
 	help