ice: declare ice_vc_process_vf_msg in ice_virtchnl.h

ice: declare ice_vc_process_vf_msg in ice_virtchnl.h

The ice_vc_process_vf_msg function is the main entry point for handling
virtchnl messages. This function is defined in ice_virtchnl.c but its
declaration is still in ice_sriov.c

The ice_sriov.c file used to contain all of the virtualization logic until
commit bf93bf791cec ("ice: introduce ice_virtchnl.c and ice_virtchnl.h")
moved the virtchnl logic to its own file.

The ice_vc_process_vf_msg function should have had its declaration moved to
ice_virtchnl.h then. Fix this.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Tested-by: Marek Szlosek <marek.szlosek@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>