Introduce three new guest commands:
guest-get-memory-blocks, guest-set-memory-blocks, guest-get-memory-block-size.

With these three commands, we can support online/offline guest's memory block
(logical memory hotplug/unplug) as required from host.
Signed-off-by: Nzhanghailiang <zhang.zhanghailiang@huawei.com>

*generalized guest-get-memory-block-size to get-get-memory-block-info
 for future extensibility
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>