Add ixgbevf driver

Driver for Intel 82599 based virtual functions.

Based on Intel's open source driver ixgbevf-2.6.2, available at:
http://sourceforge.net/projects/e1000

Based on iPXE's igbvf driver, file igbvf_main.c.

Signed-off-by: Hermann Huy <hermann.huy@nsn.com>
Signed-off-by: Bernhard Kohl <bernhard.kohl@nsn.com>