boards: intel: btl: use zephyr board sphinx directives

Improve documentation of this board by using the appropriate Sphinx
directives

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

Author: kartben

boards/intel/btl/doc/index.rst

@@ -1,7 +1,4 @@
-.. _intel_btl_s:
-
-Bartlett Lake S
-###############
+.. zephyr:board:: intel_btl_s_crb
 
 Overview
 ********
@@ -20,6 +17,8 @@ This board configuration enables kernel support for the Bartlett Lake S boards.
 Hardware
 ********
 
+.. zephyr:board-supported-hw::
+
 General information about the board can be found at the `BTL`_ website.
 
 Connections and IOs