arm64: perf: don't warn about missing interrupt-affinity property for PPIs

PPIs are affine by nature, so the interrupt-affinity property is not
used and therefore we shouldn't print a warning in its absence.

Reported-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>