mrst.c: reimplement the force cold boot properly

mrst.c: reimplement the force cold boot properly

BZ: 22672

Do a cold reset in normal case. Do a cold boot depending of module param force_cold_boot.

Change-Id: I422ac66c070f24c287fc625e1d282e2be71cbe84
Reviewed-on: http://android.intel.com:8080/34345
Reviewed-by: Kuppuswamy, Sathyanarayanan <sathyanarayanan.kuppuswamy@intel.com>
Reviewed-by: Gross, Mark <mark.gross@intel.com>
Tested-by: Ng, Cheon-woei <cheon-woei.ng@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>