drm: add missing include to fix BSD (#42)

src/backend/drm/Renderer.cpp:504:13: error: use of undeclared identifier 'close'
  504 |             close(dupFd);
      |             ^
src/backend/drm/Renderer.cpp:532:13: error: use of undeclared identifier 'close'
  532 |             close(egl.lastBlitSyncFD);
      |             ^

src/backend/drm/Renderer.cpp

@@ -3,6 +3,7 @@
 #include <xf86drmMode.h>
 #include <cstring>
 #include <fcntl.h>
+#include <unistd.h>
 #include "Math.hpp"
 #include "Shared.hpp"
 #include "FormatUtils.hpp"