kni: support userspace VA

kni: support userspace VA

Patch adds support for kernel module to work in IOVA = VA mode by
providing address translation routines to convert userspace VA to
kernel VA.

KNI performance using PA is not changed by this patch.
But comparing KNI using PA to KNI using VA, the latter will have lower
performance due to the cost of the added translation.

This translation is implemented only with kernel versions starting 4.6.0.

Signed-off-by: Vamsi Attunuru <vattunuru@marvell.com>
Signed-off-by: Kiran Kumar K <kirankumark@marvell.com>
Reviewed-by: Jerin Jacob <jerinj@marvell.com>