zimage: Don't include vboot_api.h unnecessarily.

Change-Id: I40ffdcd205b00c845caaa2db3c62ae144148244c
diff --git a/src/arch/x86/zimage.c b/src/arch/x86/zimage.c
index e4b95d6..61c3afb 100644
--- a/src/arch/x86/zimage.c
+++ b/src/arch/x86/zimage.c
@@ -22,6 +22,7 @@
 
 #include <stdint.h>
 #include <stdio.h>
+#include <string.h>
 
 #include "arch/x86/zeropage.h"
 #include "vboot/boot.h"
diff --git a/src/module/netboot.c b/src/module/netboot.c
index 8131ce8..3e4168b 100644
--- a/src/module/netboot.c
+++ b/src/module/netboot.c
@@ -21,6 +21,7 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <vboot_nvstorage.h>
 #include <vboot_api.h>
 
diff --git a/src/net/netboot/netboot.c b/src/net/netboot/netboot.c
index b78fff7..8f2ca1d 100644
--- a/src/net/netboot/netboot.c
+++ b/src/net/netboot/netboot.c
@@ -21,6 +21,8 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 
 #include "base/algorithm.h"
 #include "drivers/net/net.h"
diff --git a/src/vboot/boot.h b/src/vboot/boot.h
index 00e76af..76e1c20 100644
--- a/src/vboot/boot.h
+++ b/src/vboot/boot.h
@@ -23,8 +23,6 @@
 #ifndef __BOOT_BOOT_H__
 #define __BOOT_BOOT_H__
 
-#include <vboot_api.h>
-
 // To be implemented by each boot method.
 int boot(void *kernel, char *cmd_line, void *params, void *loader);