tools/power turbostat: Add "snapshot:" Makefile target

Kernel developers often need to diagnose remote customer systems
with the latest turbostat, yet customers are running binary distros
with out-dated turbostat and the customer has no experience
cloning linux kernel trees.

Add a turbostat "snapshot" makefile target to create a standalone
source snapshot from the developer's git tree, appropriately hacked
so that the customer can build turbostat without a kernel tree.

Include the turbostat binary in the snapshot, for convenience in
those situations where the source and destination are trusted,
(and have new enough glibc to execute).

The snapshot is named with the date it was taken rather than
the turbostat VERSION, as it could occur between VERSIONS...

Signed-off-by: Len Brown <len.brown@intel.com>