boards: shields: m5stack_core2_ext: update board name

Update documentation to meet HWMv2 naming convention.

Signed-off-by: Sylvio Alves <[email protected]>

Author: sylvioalves

boards/shields/m5stack_core2_ext/doc/index.rst

@@ -43,7 +43,7 @@ For example:
 
 .. zephyr-app-commands::
    :zephyr-app: samples/sensor/mpu6050
-   :board: m5stack_core2
+   :board: m5stack_core2/esp32/procpu
    :shield: m5stack_core2_ext
    :goals: build