KVM: PPC: Book3S HV: Report storage key support to userspace

This adds information about storage keys to the struct returned by
the KVM_PPC_GET_SMMU_INFO ioctl.  The new fields replace a pad field,
which was zeroed by previous kernel versions.  Thus userspace that
knows about the new fields will see zeroes when running on an older
kernel, indicating that storage keys are not supported.  The size of
the structure has not changed.

The number of keys is hard-coded for the CPUs supported by HV KVM,
which is just POWER7, POWER8 and POWER9.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>