device: Implement suspend/resume methods

The assumption here is that in most cases, we will just cancel any
ongoing operation. However, if the device choses to implement
suspend/resume handling and it returns success, then operations will not
be cancelled.

Note that suspend/resume requests cannot be cancelled.

Closes: #256

libfprint/fp-device-private.h

@@ -53,6 +53,7 @@ typedef struct
 
   gboolean        is_removed;
   gboolean        is_open;
+  gboolean        is_suspended;
 
   gchar          *device_id;
   gchar          *device_name;
@@ -83,6 +84,12 @@ typedef struct
   guint    critical_section;
   GSource *critical_section_flush_source;
   gboolean cancel_queued;
+  gboolean suspend_queued;
+  gboolean resume_queued;
+
+  /* Suspend/resume tasks */
+  GTask  *suspend_resume_task;
+  GError *suspend_error;
 
   /* Device temperature model information and state */
   GSource      *temp_timeout;
@@ -123,5 +130,7 @@ typedef struct
 
 void match_data_free (FpMatchData *match_data);
 
+void fpi_device_configure_wakeup (FpDevice *device,
+                                  gboolean  enabled);
 void fpi_device_update_temp (FpDevice *device,
                              gboolean  is_active);