vhost-vdpa: add uAPI for device migration status

virt inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I86ITO



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These new ioctl add support for setting vhost-vdpa device migration
state.

During migration, there is several migration state such as start/stop,
pre_start/pre_stop, post_start/post_stop, cancel etc.Some hardware needs
to do something at these stages, introduce a new ioctl to implement it.

Signed-off-by: jiangdongxu <jiangdongxu1@huawei.com>