i40e: Use the new rx ctl register helpers. Don't use AQ calls from clear_hw.

Use the new AdminQ functions for safely accessing the Rx control
registers that may be affected by heavy small packet traffic.

We can't use AdminQ calls in i40e_clear_hw() because the HW is being
initialized and the AdminQ is not alive.  We recently added an AQ
related replacement for reading PFLAN_QALLOC, and this patch puts
back the original register read.

Change-ID: Ib027168c954a5733299aa3a4ce5f8218c6bb5636
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>