ppc/xive2: Add grouping level to notification

ppc/xive2: Add grouping level to notification

The NSR has a (so far unused) grouping level field. When a interrupt
is presented, that field tells the hypervisor or OS if the interrupt
is for an individual VP or for a VP-group/crowd. This patch reworks
the presentation API to allow to set/unset the level when
raising/accepting an interrupt.

It also renames xive_tctx_ipb_update() to xive_tctx_pipr_update() as
the IPB is only used for VP-specific target, whereas the PIPR always
needs to be updated.

Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Michael Kowal <kowal@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>