sw64: kvm: add the implementation of HCALL_STOP

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I56WV8



--------------------------------

Add HCALL_STOP implementation in KVM, this exit type is used for
virtual machine CPU offline.

Signed-off-by: Lu Feifei <lufeifei@wxiat.com>
Reviewed-by: He Sheng <hesheng@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>