aspeed_sdmc: Fix saved values

aspeed_sdmc: Fix saved values

This fixes the intended protection of read-only values in the
configuration register. They were being always set to zero by mistake.

The read-only fields depend on the configured memory size of the system,
so they cannot be fixed at compile time. The most straight forward
option was to store them in the state structure.

Signed-off-by: Joel Stanley <joel@jms.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Tested-by: Cédric Le Goater <clg@kaod.org>
Message-id: 20180807075757.7242-3-joel@jms.id.au
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>