powerpc/64s: Add new set of irq_soft_mask_ functions for PMI masking

To support soft-masking of the performance monitor interrupt, a set of
new powerpc_local_irq_pmu_save() and powerpc_local_irq_restore()
functions are added. And powerpc_local_irq_save() implemented, by
adding a new irq_soft_mask manipulation function
irq_soft_mask_or_return().

Local_irq_pmu_* macros are provided to access these
powerpc_local_irq_pmu* functions which includes
trace_hardirqs_on|off() to match what we have in
include/linux/irqflags.h.

Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>