[image] Allow multiple embedded images

This patch extends the embedded image feature to allow multiple
embedded images instead of just one.

gPXE now always boots the first embedded image on startup instead of
doing the hardcoded DHCP boot (aka autoboot).

Based heavily upon a patch by Stefan Hajnoczi <stefanha@gmail.com>.

src/include/gpxe/embedded.h

@@ -1,9 +0,0 @@
-#ifndef _GPXE_EMBEDDED_H
-#define _GPXE_EMBEDDED_H
-
-#include <gpxe/image.h>
-
-struct image *embedded_image(void);
-
-#endif
-

src/include/gpxe/errfile.h

@@ -145,6 +145,7 @@
 #define ERRFILE_script		      ( ERRFILE_IMAGE | 0x00020000 )
 #define ERRFILE_segment		      ( ERRFILE_IMAGE | 0x00030000 )
 #define ERRFILE_efi_image	      ( ERRFILE_IMAGE | 0x00040000 )
+#define ERRFILE_embedded	      ( ERRFILE_IMAGE | 0x00050000 )
 
 #define ERRFILE_asn1		      ( ERRFILE_OTHER | 0x00000000 )
 #define ERRFILE_chap		      ( ERRFILE_OTHER | 0x00010000 )

src/include/gpxe/uri.h

@@ -7,6 +7,7 @@
  *
  */
 
+#include <stddef.h>
 #include <stdlib.h>
 #include <gpxe/refcnt.h>