hw/arm: ast2600: Wire up the eMMC controller

hw/arm: ast2600: Wire up the eMMC controller

Initialise another SDHCI model instance for the AST2600's eMMC
controller and use the SDHCI's num_slots value introduced previously to
determine whether we should create an SD card instance for the new slot.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-id: 20200114103433.30534-3-clg@kaod.org
[ clg : - removed ternary operator from sdhci_attach_drive()
        - renamed SDHCI objects with a '-controller' prefix ]
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>