i40e/i40evf: Pull out code for cleaning up Rx buffers

This patch pulls out the code responsible for handling buffer recycling and
page counting and distributes it through several functions.  This allows us
to commonize the bits that handle either freeing or recycling the buffers.

As far as the page count tracking one change to the logic is that
pagecnt_bias is decremented as soon as we call i40e_get_rx_buffer.  It is
then the responsibility of the function that pulls the data to either
increment the pagecnt_bias if the buffer can be recycled as-is, or to
update page_offset so that we are pointing at the correct location for
placement of the next buffer.

Change-ID: Ibac576360cb7f0b1627f2a993d13c1a8a2bf60af
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>