sparc64: add DAX2 support to dax driver

sparc64: add DAX2 support to dax driver

Orabug: 25904994

Introduce DAX2 support in the driver. This involves negotiating the right
version with hypervisor as well as exposing a new INIT_V2 ioctl. This new
ioctl will return failure if DAX2 is not present on the system, otherwise
it will attempt to initialize the DAX2. A user should first call INIT_V2
and on failure call INIT_V1. See Documentation/sparc/dax.txt for more
detail.

Signed-off-by: Jonathan Helman <jonathan.helman@oracle.com>
Reviewed-by: Sanath Kumar <sanath.s.kumar@oracle.com>
Signed-off-by: Allen Pais <allen.pais@oracle.com>