ixgbevf: convert to use of PMD_REGISTER_DRIVER and fix linking

Convert the ixgbevf pmd driver to use the PMD_REGISTER_DRIVER macro.
This means that the test applications now have no reference to the ixgbevf library
when building DSO's and must specify its use on the command line with the -d
option.  Static linking will still initalize the driver automatically.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>