crosvm/linux: use kvmclock_ctrl to signal that VCPU was suspended
crosvm/linux: use kvmclock_ctrl to signal that VCPU was suspended

On KVM implementations that use a paravirtualized clock (e.g. x86), a flag
must be set to indicate to the guest kernel that a VCPU was suspended. The
guest kernel will use this flag to prevent the soft lockup detection from
triggering when this VCPU resumes, which could happen days later in real time.

BUG=chromium:920875
TEST=inside VM `sha256sum /dev/urandom`, `crosvm suspend`, wait 30
     seconds, `crosvm resume`

Change-Id: Id479ec0c26c17499ce0d638185a79e7b19ccc69c
Reviewed-on: https://chromium-review.googlesource.com/1417190
Commit-Ready: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Tested-by: Zach Reizner <3374927928a53d04457674c546bd4de57c2044ec@chromium.org>
Reviewed-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm