libspark: add missing unistd.h includes for gcc 4.7+

libspark/dmx.cpp

@@ -61,6 +61,7 @@
 #include <poll.h>
 #include <errno.h>
 #include <inttypes.h>
+#include <unistd.h>
 
 #include <cstring>
 #include <cstdio>

libspark/playback_libeplayer3.cpp

@@ -2,6 +2,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
+#include <unistd.h>
 
 #include <audio_lib.h>
 #include <video_lib.h>