spapr_pci: Allow multiple TCE tables per PHB

spapr_pci: Allow multiple TCE tables per PHB

At the moment sPAPRPHBState contains a @tcet pointer to the only
TCE table. However sPAPR spec allows having more than one DMA window.

Since the TCE object is already a child of SPAPR PHB object, there is
no need to keep an additional pointer to it in sPAPRPHBState so remove it.

This changes the way sPAPRPHBState::reset performs reset of sPAPRTCETable
objects.

This changes the default DMA window properties calculation.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alexander Graf <agraf@suse.de>