qdev: relax bus type check in qdev_device_add() (v2)

qdev: relax bus type check in qdev_device_add() (v2)

We are currently checking for an exact type match.  Use QOM dynamic_cast to
check for a compatible type instead.

Cc: Konrad Frederic <[email protected]>
Cc: Peter Maydell <[email protected]>
Signed-off-by: Anthony Liguori <[email protected]>
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v1 -> v2:
 - also add cast to qbus_find_recursive (Peter)
 - simplify by doing object_dynamic_cast instead of messing with classes