ice: rename ice_virtchnl_pf.c to ice_sriov.c

ice: rename ice_virtchnl_pf.c to ice_sriov.c

The ice_virtchnl_pf.c and ice_virtchnl_pf.h files are where most of the
code for implementing Single Root IOV virtualization resides. This code
includes support for bringing up and tearing down VFs, hooks into the
kernel SR-IOV netdev operations, and for handling virtchnl messages from
VFs.

In the future, we plan to support Scalable IOV in addition to Single
Root IOV as an alternative virtualization scheme. This implementation
will re-use some but not all of the code in ice_virtchnl_pf.c

To prepare for this future, we want to refactor and split up the code in
ice_virtchnl_pf.c into the following scheme:

 * ice_vf_lib.[ch]

   Basic VF structures and accessors. This is where scheme-independent
   code will reside.

 * ice_virtchnl.[ch]

   Virtchnl message handling. This is where the bulk of the logic for
   processing messages from VFs using the virtchnl messaging scheme will
   reside. This is separated from ice_vf_lib.c because it is distinct
   and has a bulk of the processing code.

 * ice_sriov.[ch]

   Single Root IOV implementation, including initialization and the
   routines for interacting with SR-IOV based netdev operations.

 * (future) ice_siov.[ch]

   Scalable IOV implementation.

As a first step, lets assume that all of the code in
ice_virtchnl_pf.[ch] is for Single Root IOV. Rename this file to
ice_sriov.c and its header to ice_sriov.h

Future changes will further split out the code in these files following
the plan outlined here.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>