sparc64: Detect DAX ra+pgsz when hvapi minor doesn't indicate it

sparc64: Detect DAX ra+pgsz when hvapi minor doesn't indicate it

Orabug: 25911008

The RA+PGSZ HV API feature is detected via a controlled experiment.
The experiment constructs a small DAX request and places the output
buffer at the very end of an 8k page. Then it checks to see if the 8k
page boundary was honored, and if so, then we've got the ability to pass
the page size along with a real address. Once the HV API minor number
is bumped to 1, this will be the primary method of detection.

Signed-off-by: Rob Gardner <rob.gardner@oracle.com>
Reviewed-by: Jonathan Helman <jonathan.helman@oracle.com>
(cherry picked from commit 013d5b9909e804817dcd939f50f242f09237feac)
Signed-off-by: Allen Pais <allen.pais@oracle.com>