powercap / RAPL: add support for CPU model 0x3f

I've confirmed that monitoring the package power usage as well as setting power
limits appear to be working as expected. Supports the package and dram domains.

Tested aginst cpu:

Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz

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