Remove unneeded #include statements completely

Unistd.h was only used to get a definition of NULL in all files. Add our
own NULL #define and remove unistd.h from flash.h
stdio.h has no place in flash.h, it should be included only in files
which really need it.
Add #include statements in individual .c files where needed.

Replace a few printf with msg_* to eliminate the need for stdio.h.

Corresponding to flashrom svn r1021.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Uwe Hermann <uwe@hermann-uwe.de>
diff --git a/udelay.c b/udelay.c
index bae6467..9c7a673 100644
--- a/udelay.c
+++ b/udelay.c
@@ -19,6 +19,7 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  */
 
+#include <unistd.h>
 #include <sys/time.h>
 #include <stdlib.h>
 #include <limits.h>
@@ -63,7 +64,7 @@
 	unsigned long timeusec;
 	int i, tries = 0;
 
-	printf("Calibrating delay loop... ");
+	msg_pinfo("Calibrating delay loop... ");
 
 recalibrate:
 	count = 1000;
@@ -113,7 +114,7 @@
 	timeusec = measure_delay(10000);
 	msg_pdbg("10000 myus = %ld us, ", timeusec);
 
-	printf("OK.\n");
+	msg_pinfo("OK.\n");
 }
 
 void internal_delay(int usecs)