KVM: arm64: vgic-v5: Limit support to 64 PPIs

KVM: arm64: vgic-v5: Limit support to 64 PPIs

Although we have some code supporting 128 PPIs, the only supported
configuration is 64 PPIs. There is no way to test the 128 PPI code,
so it is bound to bitrot very quickly.

Given that KVM/arm64's goal has always been to stick to non-IMPDEF
behaviours, drop the 128 PPI support. Someone motivated enough and
with very strong arguments can always bring it back -- it's all in
the git history.

Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20260520091949.542365-10-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>