Signal hw keyboard availability state over D-Bus System Bus

Classify evdev nodes that send KEY_Q and KEY_P events as keyboards
or slide-in keypads depending on whether they also emit SW_KEYPAD_SLIDE
switch state events.

Maintain a hw-keyboard-is-available state - which is true as long as
there exists at least one keyboard device or slide-in keypad in open
position.

When availability state changes, a keypad_available_state_ind signal
is broadcast over D-Bus System Bus.

<node name="/com/nokia/mce/signal">
  <interface name="com.nokia.mce.signal">
    <signal name="keypad_available_state_ind">
      <arg name="keypad_state" type="s"/>
    </signal>
  </interface>
</node>

Current state can be queried from mce with keypad_available_state_req
D-Bus method call.

<node name="/com/nokia/mce/request">
  <interface name="com.nokia.mce.request">
    <method name="keypad_available_state_req">
      <arg direction="out" name="keypad_state" type="s"/>
    </method>
  </interface>
</node>

[mce] Signal hw keyboard availability state over D-Bus System Bus. Fixes JB#25232

datapipe.c

@@ -82,6 +82,9 @@ datapipe_struct lockkey_pipe;
 /** Keyboard open/closed; read only */
 datapipe_struct keyboard_slide_pipe;
 
+/** Keyboard available; read only */
+datapipe_struct keyboard_available_pipe;
+
 /** Lid cover open/closed; read only */
 datapipe_struct lid_cover_pipe;
 
@@ -823,6 +826,8 @@ void mce_datapipe_init(void)
 		       0, GINT_TO_POINTER(0));
 	setup_datapipe(&keyboard_slide_pipe, READ_ONLY, DONT_FREE_CACHE,
 		       0, GINT_TO_POINTER(COVER_CLOSED));
+	setup_datapipe(&keyboard_available_pipe, READ_ONLY, DONT_FREE_CACHE,
+		       0, GINT_TO_POINTER(COVER_CLOSED));
 	setup_datapipe(&lid_cover_pipe, READ_ONLY, DONT_FREE_CACHE,
 		       0, GINT_TO_POINTER(COVER_OPEN));
 	setup_datapipe(&lens_cover_pipe, READ_ONLY, DONT_FREE_CACHE,
@@ -902,6 +907,7 @@ void mce_datapipe_quit(void)
 	free_datapipe(&lens_cover_pipe);
 	free_datapipe(&lid_cover_pipe);
 	free_datapipe(&keyboard_slide_pipe);
+	free_datapipe(&keyboard_available_pipe);
 	free_datapipe(&lockkey_pipe);
 	free_datapipe(&device_inactive_pipe);
 	free_datapipe(&touchscreen_pipe);

datapipe.h

@@ -106,6 +106,7 @@ extern datapipe_struct keypress_pipe;
 extern datapipe_struct touchscreen_pipe;
 extern datapipe_struct lockkey_pipe;
 extern datapipe_struct keyboard_slide_pipe;
+extern datapipe_struct keyboard_available_pipe;
 extern datapipe_struct lid_cover_pipe;
 extern datapipe_struct lens_cover_pipe;
 extern datapipe_struct proximity_sensor_pipe;