ice: configure GLINT_ITR to always have an ITR gran of 2

Instead of hoping that our ITR granularity will be 2 usec program the
GLINT_CTL register to make sure the ITR granularity is always 2 usecs.

Now that we know what the ITR granularity will be get rid of the check
in ice_probe() to verify our previous assumption.

Signed-off-by: Brett Creeley <brett.creeley@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>