hw/sd: Configure number of slots exposed by the ASPEED SDHCI model

hw/sd: Configure number of slots exposed by the ASPEED SDHCI model

The AST2600 includes a second cut-down version of the SD/MMC controller
found in the AST2500, named the eMMC controller. It's cut down in the
sense that it only supports one slot rather than two, but it brings the
total number of slots supported by the AST2600 to three.

The existing code assumed that the SD controller always provided two
slots. Rework the SDHCI object to expose the number of slots as a
property to be set by the SoC configuration.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-id: 20200114103433.30534-2-clg@kaod.org
[PMM: fixed up to use device_class_set_props()]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>