boards: renesas: Edit rcar_salvator_x full_name

Edit the rcar_salvator_x board full_name
to meet names used by other rcar board
and unify this board range documentation.

Signed-off-by: Aymeric Aillet <aymeric.aillet@iot.bzh>

Author: aaillet

boards/renesas/rcar_salvator_x/board.yml

@@ -1,6 +1,6 @@
 board:
   name: rcar_salvator_x
-  full_name: R-Car H3 Salvator-X
+  full_name: R-Car Salvator-X
   vendor: renesas
   socs:
   - name: r8a77951