aspeed: Deprecate the fby35 machine

aspeed: Deprecate the fby35 machine

There are no functional tests for the 'fby35' machine which makes
harder to determine when something becomes deprecated or unused.

The 'fby35' machine was originally added as an example of a multi-SoC
system, with the expectation the models would evolve over time in an
heterogeneous system. This hasn't happened and no public firmware is
available to boot it. It can be replaced by the 'ast2700fc', another
multi-SoC machine based on the newer AST2700 SoCs which are excepted
to receive better support in the future.

Cc: Peter Delevoryas <peter@pjd.dev>
Signed-off-by: Cédric Le Goater <clg@redhat.com>
Message-ID: <20251126102424.927527-1-clg@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>