[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/core/config.c

@@ -218,3 +218,4 @@ REQUIRE_OBJECT ( gdbstub_cmd );
  *
  */
 REQUIRE_OBJECT ( device );
+REQUIRE_OBJECT ( embedded );