kvm: Convert kvm_lock to a mutex

kvm: Convert kvm_lock to a mutex

It doesn't seem as if there is any particular need for kvm_lock to be a
spinlock, so convert the lock to a mutex so that sleepable functions (in
particular cond_resched()) can be called while holding it.

Signed-off-by: Junaid Shahid <junaids@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
CVE-2018-12207

(backported from commit 0d9ce162cf46c99628cc5da9510b959c7976735b)
[tyhicks: Backport to 4.15
 - kvm_hyperv_tsc_notifier() does not exist]
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>