plugins: fix order of init/idle/resume callback

plugins: fix order of init/idle/resume callback

We found that vcpu_init_hook was called *after* idle callback.
vcpu_init is called from cpu_realize_fn, while idle/resume cb are called
from qemu_wait_io_event (in vcpu thread).

This change ensures we only call idle and resume cb only once a plugin
was init for a given vcpu.

Next change in the series will run vcpu_init asynchronously, which will
make it run *after* resume callback as well. So we fix this now.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20240213094009.150349-4-pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240227144335.1196131-18-alex.bennee@linaro.org>