A common use case for the ASPEED machine is to boot a Linux kernel.
Provide a full example command line.

Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Message-id: 20211117065752.330632-4-joel@jms.id.au
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>