KVM: polling: add architecture backend to disable polling

mainline inclusion
from mainline-5.2
commit cdd6ad3a
category: feature
bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=34


CVE: NA

There are cases where halt polling is unwanted. For example when running
KVM on an over committed LPAR we rather want to give back the CPU to
neighbour LPARs instead of polling. Let us provide a callback that
allows architectures to disable polling.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Yubo Miao <miaoyubo@huawei.com>
Signed-off-by: Xiangyou Xie <xiexiangyou@huawei.com>
Reviewed-by: Hailiang Zhang <zhang.zhanghailiang@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Jiajun Chen <chenjiajun8@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>