fb2png: Update/Cleanup headers

* Include relevant headers for all used functions
* Add prototype for fb_dump() to fb.h since used in c-files
* Alphabetize includes

Change-Id: Ifdbaceadb12576b607b654835ae93bc88e2c3268
diff --git a/fb2png/main.c b/fb2png/main.c
index 84e08a9..235e958 100644
--- a/fb2png/main.c
+++ b/fb2png/main.c
@@ -17,9 +17,12 @@
  * with this program; if not, write to the Free Software Foundation, Inc.,
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
-#include <stdio.h>
+
 #include <limits.h>
+#include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
+
 #include "fb2png.h"
 
 #ifdef ANDROID