powerpc/eeh: Allow to freeze PE in eeh_pe_set_option()

Function eeh_pe_set_option() is used to apply the requested options
(enable, disable, unfreeze) in EEH virtualization path. The semantics
of this function isn't complete until freezing is supported.

This allows to freeze the indicated PE. The new semantics is going to
be used in PCI surprise hot remove path, to freeze removed PCI devices
(PE) to avoid unexpected EEH error reporting.

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