tools/power turbostat: correct DRAM RAPL units on recent Xeon processors

While not yet documented in the Software Developer's Manual,
the data-sheet for modern Xeon states that DRAM RAPL ENERGY units
are fixed at 15.3 uJ, rather than being discovered via MSR.

Before this patch, DRAM energy on these products is over-stated by turbostat
because the RAPL units are 4x larger.

ref: "Xeon E5-2600 v3/E5-1600 v3 Datasheet Volume 2"
http://www.intel.com/content/dam/www/public/us/en/documents/datasheets/xeon-e5-v3-datasheet-vol-2.pdf



Signed-off-by: Andrey Semin <andrey.semin@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>