Use of headers from other dsme development packages requires e.g.

  #include <dsme/state.h>

To avoid conflicts with includes with generic names, make it so that
the same is required for dsme-plugin headers, e.g.

  #include <dsme-plugin/modules.h>
Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>