fp-device: Move fpi code into its own unit that can be compiled a part

In order to be able to test the private device code (used by drivers) we
need to have that split a part in a different .c file so that we can compile
it alone and link with it both the shared library and the test executables.

Redefine fp_device_get_instance_private for private usage, not to move
the private struct as part of FpDevice.

libfprint/fp-device-private.h

@@ -0,0 +1,65 @@
+/*
+ * FpDevice - A fingerprint reader device
+ * Copyright (C) 2019 Benjamin Berg <bberg@redhat.com>
+ * Copyright (C) 2019 Marco Trevisan <marco.trevisan@canonical.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#pragma once
+
+#include "fpi-device.h"
+
+typedef struct
+{
+  FpDeviceType type;
+
+  GUsbDevice  *usb_device;
+  const gchar *virtual_env;
+
+  gboolean     is_open;
+
+  gchar       *device_id;
+  gchar       *device_name;
+  FpScanType   scan_type;
+
+  guint64      driver_data;
+
+  gint         nr_enroll_stages;
+  GSList      *sources;
+
+  /* We always make sure that only one task is run at a time. */
+  FpDeviceAction      current_action;
+  GTask              *current_task;
+  GAsyncReadyCallback current_user_cb;
+  gulong              current_cancellable_id;
+  GSource            *current_idle_cancel_source;
+  GSource            *current_task_idle_return_source;
+
+  /* State for tasks */
+  gboolean wait_for_finger;
+} FpDevicePrivate;
+
+
+typedef struct
+{
+  FpPrint         *print;
+
+  FpEnrollProgress enroll_progress_cb;
+  gpointer         enroll_progress_data;
+  GDestroyNotify   enroll_progress_destroy;
+} FpEnrollData;
+
+void enroll_data_free (FpEnrollData *enroll_data);

libfprint/meson.build

@@ -8,6 +8,7 @@ libfprint_sources = [
 
 libfprint_private_sources = [
     'fpi-assembling.c',
+    'fpi-device.c',
     'fpi-ssm.c',
     'fpi-usb-transfer.c',
     'fpi-byte-reader.c',