x86: add PAT related debug prints

Adds debug prints at critical code. Adds enough info in dmesg to allow us to
do effective first round of analysis of any issues that may result due to PAT
patch series.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>