feat(qemu): increase max cpus per cluster to 16

feat(qemu): increase max cpus per cluster to 16

Qemu-tcg with GICv3 emulation enabled will by default configure MPIDR
topology to report up to 16 cpus per cluster. This is NOT overriden by
qemu's -smp setting, e.g. -smp 8,clusters=2,cores=4,threads=1 will still
generate MPIDR reads as if all 8 CPUs were within one cluster.

Increase the hardcoded limit to reflect that so that we accept PSCI
calls that provide MPIDRs based on what was actually read from the
emulated CPU.

Change-Id: Ia321d555f885c96a9a94ae053b340e3a9e300e6d
Signed-off-by: Evgeny Iakovlev <eiakovlev@linux.microsoft.com>