aspeed/smc: Add support for DMAs

The FMC controller on the Aspeed SoCs support DMA to access the flash
modules. It can operate in a normal mode, to copy to or from the flash
module mapping window, or in a checksum calculation mode, to evaluate
the best clock settings for reads.

The model introduces two custom address spaces for DMAs: one for the
AHB window of the FMC flash devices and one for the DRAM. The latter
is populated using a "dram" link set from the machine with the RAM
container region.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Acked-by: Joel Stanley <joel@jms.id.au>
Message-id: 20190904070506.1052-6-clg@kaod.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>