powerpc/powernv: Handle compound PE for EEH

The patch handles compound PE for EEH backend. If one specific
PE in compound group has been frozen, we enforces to freeze
all PEs in the group. If we're enable DMA or MMIO for one PE
in compound group, DMA or MMIO of all PEs in the group will be
enabled.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>