Drivers: hv: vmbus: Suspend/resume the synic for hibernation

This is needed when we resume the old kernel from the "current" kernel.

Note: when hv_synic_suspend() and hv_synic_resume() run, all the
non-boot CPUs have been offlined, and interrupts are disabled on CPU0.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>