x86: Remove usage of %ebp as a return pointer

Using %ebp as a return pointer prevents creating 'load anywhere' images
diff --git a/board/eNET/eNET_start16.S b/board/eNET/eNET_start16.S
index af2c132..06cfd55 100644
--- a/board/eNET/eNET_start16.S
+++ b/board/eNET/eNET_start16.S
@@ -65,8 +65,7 @@
 	movl	$0x000000cb, %eax
 	outl	%eax, %dx
 
-	/* the return address is stored in bp */
-	jmp	*%bp
+	jmp	board_init16_ret
 
 .section .bios, "ax"
 .code16