Split sunvnet.c into sunvnet.c and sunvnet_common.c.

  Details:

  Since the sunvnet and ldmvsw drivers will both use common sunvnet code,
  move the functions (and support functions) anticipated to be common code
  from sunvnet.c to sunvnet_common.c. Similarly, sunvnet.h was renamed to
  sunvnet_common.h. The sunvnet_common.c code will be compiled into the
  kernel and act as a library of functions that are linked by either
  (or both) drivers when loaded.

  Function names for external functions in sunvnet_common.c (to be
  called by both the sunvnet and ldmvsw drivers) were tagged with a "_common"
  suffix to clearly designate them as common functions.

  No functional changes as of yet... just moved code verbatim to the new
  sunvnet_common.c/h files.

  Makefile/Kconfig support added to build sunvnet_common.c file. The code
  is included in the kernel if SUN_LDOMS is defined/selected.

  NOTE - per the SubmittingPatches documentation, since the code was just
  moved from one file another, the code was NOT checkpatch'd in this commit
  to aid in review.

  Signed-off-by: Aaron Young <aaron.young@oracle.com>
  Signed-off-by: Rashmi Narasimhan <rashmi.narasimhan@oracle.com>
  Reviewed-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
  Reviewed-by: Alexandre Chartre <Alexandre.Chartre@oracle.com>

Signed-off-by: David S. Miller <davem@davemloft.net>