e1000e: cleanup indexed register arrays

Some Rx and Tx specific registers are arrays indexed by the queue number.
For clarity, specify the intended queue rather than obscuring it behind a
define.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>