powerpc/powernv: Unfreeze PE on allocation

This unfreezes PE when it's initialized because the PE might be put
into frozen state in the last hot remove path. It's not harmful to
do so if the PE is already in unfrozen state.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>