drivers/net/ethernet: Add ethernet dir and config option

This is the initial patch to organize the drivers/net directory
structure and networking device driver config options.  This patch
does the following:
  - add drivers/net/ethernet/Kconfig
  - integrate the new files into the existing config

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
diff --git a/drivers/net/Makefile b/drivers/net/Makefile
index e1eca2a..670b514 100644
--- a/drivers/net/Makefile
+++ b/drivers/net/Makefile
@@ -1,5 +1,5 @@
 #
-# Makefile for the Linux network (ethercard) device drivers.
+# Makefile for the Linux network device drivers.
 #
 
 obj-$(CONFIG_MII) += mii.o