hw/core/qdev: update hotplug reset regarding resettable

hw/core/qdev: update hotplug reset regarding resettable

This commit make use of the resettable API to reset the device being
hotplugged when it is realized. Also it ensures it is put in a reset
state coherent with the parent it is plugged into.

Note that there is a difference in the reset. Instead of resetting
only the hotplugged device, we reset also its subtree (switch to
resettable API). This is not expected to be a problem because
sub-buses are just realized too. If a hotplugged device has any
sub-buses it is logical to reset them too at this point.

The recently added should_be_hidden and PCI's partially_hotplugged
mechanisms do not interfere with realize operation:
+ In the should_be_hidden use case, device creation is
delayed.
+ The partially_hotplugged mechanism prevents a device to be
unplugged and unrealized from qdev POV and unrealized.

Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200123132823.1117486-8-damien.hedde@greensocs.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>