Set the ITR max and min values to match the hardware max value
and the recommended min value.  These values are shifted right
one bit because the register counts in 2 usec units, so leave
a comment to explain.

Change-ID: I289c27955cf6c566a6d21b95c3110b88cbb15dad
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Kavindya Deegala <kavindya.s.deegala@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>