i40e/i40evf: Refactor i40e_debug_aq and make some functions static

i40e/i40evf: Refactor i40e_debug_aq and make some functions static

A sparse complaint in i40e_debug_aq in a funky buffer write goes away by
straightening out the code out to something less convoluted.

Also fix some other sparse warnings while we are at it, making some
functions static and using NULL instead of 0.

Change-ID: I93907534fe1f1f675830774b3d14ecf1c6ffc9a0
Signed-off-by: Shannon Nelson <shannon.nelson@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>