Fix and improve libpayload platform support

- Fix various minor compile issues (eg. include necessary standard headers)
- Fix compilation of libpayload code paths
- Provide libpayload support in Makefile
- Add make target "libflashrom.a" which links non-CLI code to static
  library

Corresponding to flashrom svn r1280.

Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Tested-with-DOS-crosscompiler-by: Idwer Vollering <vidwer@gmail.com>
Acked-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>

spi.c

@@ -22,6 +22,7 @@
  * Contains the generic SPI framework
  */
 
+#include <strings.h>
 #include <string.h>
 #include "flash.h"
 #include "flashchips.h"