Implement libpayload support and improve life for DOS based flashrom, too

Corresponding to flashrom svn r1181.

Change the physmap* behaviour to use (void*)-1 as error code instead
of NULL. That way, 1:1 mapped memory can be supported properly
because (void*)0 is not a magic pointer anymore.
(void*)-1 on the other hand is a rather unlikely memory offset, so that
should be safe.
  
Signed-off-by: Patrick Georgi <patrick.georgi@coresystems.de>
Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>

flash.h

@@ -33,6 +33,8 @@
 #undef max
 #endif
 
+#define ERROR_PTR ((void*)-1)
+
 typedef unsigned long chipaddr;
 
 int register_shutdown(void (*function) (void *data), void *data);