KVM: Rename and add argument to check_extension

In preparation to make the check_extension function available to VM scope
we add a struct kvm * argument to the function header and rename the function
accordingly. It will still be called from the /dev/kvm fd, but with a NULL
argument for struct kvm *.

Signed-off-by: Alexander Graf <agraf@suse.de>
KVM: Allow KVM_CHECK_EXTENSION on the vm fd

The KVM_CHECK_EXTENSION is only available on the kvm fd today. Unfortunately
on PPC some of the capabilities change depending on the way a VM was created.

So instead we need a way to expose capabilities as VM ioctl, so that we can
see which VM type we're using (HV or PR). To enable this, add the
KVM_CHECK_EXTENSION ioctl to our vm ioctl portfolio.

Signed-off-by: Alexander Graf <agraf@suse.de>
KVM: PPC: Book3S: Provide different CAPs based on HV or PR mode

With Book3S KVM we can create both PR and HV VMs in parallel on the same
machine. That gives us new challenges on the CAPs we return - both have
different capabilities.

When we get asked about CAPs on the kvm fd, there's nothing we can do. We
can try to be smart and assume we're running HV if HV is available, PR
otherwise. However with the newly added VM CHECK_EXTENSION we can now ask
for capabilities directly on a VM which knows whether it's PR or HV.

With this patch I can successfully expose KVM PVINFO data to user space
in the PR case, fixing magic page mapping for PAPR guests.

Signed-off-by: Alexander Graf <agraf@suse.de>