arm, config: Add an example ARM big.LITTLE(tm) configuration script

arm, config: Add an example ARM big.LITTLE(tm) configuration script

An ARM big.LITTLE system consists of two cpu clusters: the big
CPUs are typically complex out-of-order cores and the little
CPUs are simpler in-order ones. The fs_bigLITTLE.py script
can run a full system simulation with various number of big
and little cores and cache hierarchy. The commit also includes
two example device tree files for booting Linux on the
bigLITTLE system.

Change-Id: I6396fb3b2d8f27049ccae49d8666d643b66c088b
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>