plugins: Check if vCPU is realized

plugins: Check if vCPU is realized

The created member of CPUState tells if the vCPU thread is started, and
will be always false for the user space emulation that manages threads
independently. Use the realized member of DeviceState, which is valid
for both of the system and user space emulation.

Fixes: 54cb65d858 ("plugin: add core code")
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Message-Id: <20230912224107.29669-4-akihiko.odaki@daynix.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231009164104.369749-11-alex.bennee@linaro.org>