boards: seagate: legend: Add board revision configurations

board.yml file was missing the list of custom revisions of this board.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>
(cherry picked from commit 9c803c02b59fc25dfc20431d29b4ee4d1f401dc7)
diff --git a/boards/seagate/legend/board.yml b/boards/seagate/legend/board.yml
index a015c60..e478092 100644
--- a/boards/seagate/legend/board.yml
+++ b/boards/seagate/legend/board.yml
@@ -4,5 +4,10 @@
   vendor: seagate
   revision:
     format: custom
+    default: "25hdd"
+    revisions:
+      - name: "25hdd"
+      - name: "25ssd"
+      - name: "35"
   socs:
     - name: stm32f070xb