i40evf: driver core headers

This patch contains the main driver header files, containing structures
and data types specific to the linux driver.

i40e_osdep.h contains some code that helps us adapt our OS agnostic code
to Linux.

Signed-off-by: Mitch Williams <mitch.a.williams@intel.com>
Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>