KVM: Resync only arch fields when slots_arch_lock gets reacquired

KVM: Resync only arch fields when slots_arch_lock gets reacquired

There is no need to copy the whole memslot data after releasing
slots_arch_lock for a moment to install temporary memslots copy in
kvm_set_memslot() since this lock only protects the arch field of each
memslot.

Just resync this particular field after reacquiring slots_arch_lock.

Note, this also eliminates the need to manually clear the INVALID flag
when restoring memslots; the "setting" of the INVALID flag was an
unwanted side effect of copying the entire memslots.

Since kvm_copy_memslots() has just one caller remaining now
open-code it instead.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
[sean: tweak shortlog, note INVALID flag in changelog, revert comment]
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <b63035d114707792e9042f074478337f770dff6a.1638817638.git.maciej.szmigiero@oracle.com>