ice: introduce ice_vf_lib.c, ice_vf_lib.h, and ice_vf_lib_private.h

ice: introduce ice_vf_lib.c, ice_vf_lib.h, and ice_vf_lib_private.h

Introduce the ice_vf_lib.c file along with the ice_vf_lib.h and
ice_vf_lib_private.h header files.

These files will house the generic VF structures and access functions.
Move struct ice_vf and its dependent definitions into this new header
file.

The ice_vf_lib.c is compiled conditionally on CONFIG_PCI_IOV. Some of
its functionality is required by all driver files. However, some of its
functionality will only be required by other files also conditionally
compiled based on CONFIG_PCI_IOV.

Declaring these functions used only in CONFIG_PCI_IOV files in
ice_vf_lib.h is verbose. This is because we must provide a fallback
implementation for each function in this header since it is included in
files which may not be compiled with CONFIG_PCI_IOV.

Instead, introduce a new ice_vf_lib_private.h header which verifies that
CONFIG_PCI_IOV is enabled. This header is intended to be directly
included in .c files which are CONFIG_PCI_IOV only. Add a #error
indication that will complain if the file ever gets included by another
C file on a kernel with CONFIG_PCI_IOV disabled. Add a comment
indicating the nature of the file and why it is useful.

This makes it so that we can easily define functions exposed from
ice_vf_lib.c into other virtualization files without needing to add
fallback implementations for every single function.

This begins the path to separate out generic code which will be reused
by other virtualization implementations from ice_sriov.h and ice_sriov.c

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>