spapr: Remove unnecessary instance_size specifications from DRC subtypes

All the DRC subtypes explicitly list instance_size in TypeInfo (all as
sizeof(sPAPRDRConnector).  This isn't necessary, since if it's not listed
it will be derived from the parent type.

Worse, this is dangerous, because if a subtype is changed in future to
have a larger structure, then subtypes of that subtype also need to have
instance_size changed, or it will lead to hard to track memory corruption
bugs.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
