Modify multithreaded dts file of DynamIQ FVPs

The dts file now contains a CPU map that precisely describes the
topology including thread nodes. The map was also extended to have 16
PEs to be able to test multithreaded FVPs with 8 cores in the same
cluster.

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: If39559b05d20bfd68d0ecf830ddcbc5233b288a0