powerpc/cell: Disable ptcal in case of crash kdump

We need to disable ptcal before starting a new kernel after a crash,
in order to avoid overwriting data in the kdump kernel.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>