KVM: x86: Move CPU compat checks hook to kvm_x86_ops (from kvm_x86_init_ops)

Move the .check_processor_compatibility() callback from kvm_x86_init_ops
to kvm_x86_ops to allow a future patch to do compatibility checks during
CPU hotplug.

Do kvm_ops_update() before compat checks so that static_call() can be
used during compat checks.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Message-Id: <20221130230934.1014142-40-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>