It cleanups the current models for the Aspeed AST2400 and AST2500 SoCs
and prepares ground for future SoCs.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Message-id: 20190925143248.10000-11-clg@kaod.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>