sd/pxa2xx_mmci: Fix to realize "pxa2xx-mmci" device

sd/pxa2xx_mmci: Fix to realize "pxa2xx-mmci" device

pxa2xx_mmci_init() creates a "pxa2xx-mmci" device, but neglects to
realize it.  Affects machines akita, borzoi, connex, mainstone, spitz,
terrier, tosa, verdex, and z2.

In theory, a device becomes real only on realize.  In practice, the
transition from unreal to real is a fuzzy one.  The work to make a
device real can be spread between realize methods (fine),
instance_init methods (wrong), and board code wiring up the device
(fine as long as it effectively happens on realize).  Depending on
what exactly is done where, a device can work even when we neglect
to realize it.

This one appears to work.  Nevertheless, it's a clear misuse of the
interface.  Even when it works today (more or less by chance), it can
break tomorrow.

Fix by realizing it right away.  Visible in "info qom-tree"; here's
the change for akita:

     /machine (akita-machine)
       [...]
       /unattached (container)
         [...]
    +    /device[5] (pxa2xx-mmci)
    +      /pxa2xx-mmci[0] (qemu:memory-region)
    +      /sd-bus (pxa2xx-mmci-bus)
         [rest of device[*] renumbered...]

Fixes: 7a9468c92517e19037bfe2272f64f5dadaf9db15
Cc: Andrzej Zaborowski <balrogg@gmail.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-arm@nongnu.org
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200609122339.937862-4-armbru@redhat.com>