powercap / RAPL: add support for ValleyView Soc

This patch adds support for RAPL on Intel ValleyView based SoC
platforms, such as Baytrail.

Besides adding CPU ID, special energy unit encoding is handled
for ValleyView.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>