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

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

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

boards/alientek/pandora_stm32l475/doc/index.rst

@@ -1,7 +1,4 @@
-.. _pandora_stm32l475_board:
-
-Alientek STM32L475 Pandora
-##########################
+.. zephyr:board:: pandora_stm32l475
 
 Overview
 ********
@@ -28,15 +25,12 @@ some highlights of the STM32L475 Pandora board:
 - MCU current ammeter with 4 ranges and auto-calibration
 - Connector for external board or RF-EEPROM
 - Four power supply options:
+
     - ST-LINK/V2-1
     - USB FS connector
     - External 5 V
     - CR2032 battery (not provided)
 
-.. image:: img/pandora_stm32l475.jpg
-     :align: center
-     :alt: STM32L475 Pandora
-
 More information about the board can be found at the `STM32L475 Pandora website`_.
 
 Hardware