spapr_drc: don't allow 'empty' DRCs to be unisolated or allocated

spapr_drc: don't allow 'empty' DRCs to be unisolated or allocated

Logical resources start with allocation-state:UNUSABLE /
isolation-state:ISOLATED. During hotplug, guests will transition
them to allocation-state:USABLE, and then to
isolation-state:UNISOLATED.

For cases where we cannot transition to allocation-state:USABLE,
in this case due to no device/resource being association with
the logical DRC, we should return an error -3.

For physical DRCs, we default to allocation-state:USABLE and stay
there, so in this case we should report an error -3 when the guest
attempts to make the isolation-state:ISOLATED transition for a DRC
with no device associated.

These are as documented in PAPR 2.7, 13.5.3.4.

We also ensure allocation-state:USABLE when the guest attempts
transition to isolation-state:UNISOLATED to deal with misbehaving
guests attempting to bring online an unallocated logical resource.

This is as documented in PAPR 2.7, 13.7.

Currently we implement no such error logic. Fix this by handling
these error cases as PAPR defines.

Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>