boards: element14: adopt new zephyr:board directive and role

This updates the documentation of all the Element14 boards
to use the new `zephyr:board::` directive.

Signed-off-by: Benjamin Cabé <[email protected]>

Author: kartben

boards/element14/warp7/doc/index.rst

@@ -1,7 +1,4 @@
-.. _warp7:
-
-WaRP7 - Next Generation IoT and Wearable Development Platform
-#############################################################
+.. zephyr:board:: warp7
 
 Overview
 ********
@@ -11,11 +8,6 @@ core and Single Cortex M4 core.
 Zephyr was ported to run on the M4 core. In a later release, it will also
 communicate with the A7 core (running Linux) via RPmsg.
 
-
-.. image:: warp7.jpg
-   :align: center
-   :alt: WaRP7-iMX7S
-
 Hardware
 ********