ppc/xive2: Support group-matching when looking for target

ppc/xive2: Support group-matching when looking for target

If an END has the 'i' bit set (ignore), then it targets a group of
VPs. The size of the group depends on the VP index of the target
(first 0 found when looking at the least significant bits of the
index) so a mask is applied on the VP index of a running thread to
know if we have a match.

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>