Move memmap.h out of arch/i386; it no longer contains anything

architecture-dependent and is needed by the ELF code.

src/arch/i386/core/relocate.c

 #include <io.h>
 #include <registers.h>
-#include <memmap.h>
+#include <gpxe/memmap.h>
 
 /*
  * Originally by Eric Biederman

src/arch/i386/firmware/pcbios/memmap.c

 #include <errno.h>
 #include <realmode.h>
 #include <bios.h>
-#include <memmap.h>
+#include <gpxe/memmap.h>
 
 /**
  * @file

src/arch/i386/include/memmap.h → src/include/gpxe/memmap.h

-#ifndef _MEMMAP_H
-#define _MEMMAP_H
+#ifndef _GPXE_MEMMAP_H
+#define _GPXE_MEMMAP_H
 
 #include <stdint.h>
 
 
 extern void get_memmap ( struct memory_map *memmap );
 
-#endif /* _MEMMAP_H */
+#endif /* _GPXE_MEMMAP_H */