Introduce netdev.h header file and remove externs

This addresses all drivers whose initializers have already
been moved to board_eth_init()/cpu_eth_init().

Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
diff --git a/board/atmel/atngw100/atngw100.c b/board/atmel/atngw100/atngw100.c
index 7f3e485..fa1a2aa 100644
--- a/board/atmel/atngw100/atngw100.c
+++ b/board/atmel/atngw100/atngw100.c
@@ -26,6 +26,7 @@
 #include <asm/arch/clk.h>
 #include <asm/arch/gpio.h>
 #include <asm/arch/hmatrix.h>
+#include <netdev.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -93,8 +94,6 @@
 	gd->bd->bi_phy_id[1] = 0x03;
 }
 
-extern int macb_eth_initialize(int id, void *regs, unsigned int phy_addr);
-
 #ifdef CONFIG_CMD_NET
 int board_eth_init(bd_t *bi)
 {