docs: aspeed: Add fby35 board

Add fby35 to the list of Aspeed boards.

Signed-off-by: Peter Delevoryas <pdel@fb.com>
Message-Id: <20220506193354.990532-2-pdel@fb.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>

docs/system/arm/aspeed.rst

@@ -31,6 +31,7 @@ AST2600 SoC based machines :
 - ``tacoma-bmc``           OpenPOWER Witherspoon POWER9 AST2600 BMC
 - ``rainier-bmc``          IBM Rainier POWER10 BMC
 - ``fuji-bmc``             Facebook Fuji BMC
+- ``fby35-bmc``            Facebook fby35 BMC
 
 Supported devices
 -----------------