mem: Fix search-replace issues in DRAMPower wrapper license

Fix a number of unintentional insertions of 'const'.

mem: Add DRAMPower wrapping class

This patch adds a class to wrap DRAMPower Library in gem5.
This class initiates an object of class MemorySpecification
of the DRAMPower Library, passes the parameters from DRAMCtrl.py
to this object and creates an object of drampower library using
the memory specification.