sparc64: disable dax page range checking on RA

sparc64: disable dax page range checking on RA

Orabug: 25820812

This fix is to address a hypervisor f/w change which affects
T7 machines with 3.0 cpu and T8 machines. Newer HV f/w
pays attention to the page size field in real addresses.
This is not a bug; I asked them to implement this long ago.
A value of zero here means 8k, so RA buffers are restricted
to one page when running on newer firmware. The PRM defines a page
size of 0xF to mean "disable page range checking". We set this
value for all real addresses. Old f/w will overwrite this field
anyway, so it's safe for us to always set it.

Signed-off-by: Rob Gardner <rob.gardner@oracle.com>
Reviewed-by: Jonathan Helman <jonathan.helman@oracle.com>
Signed-off-by: Allen Pais <allen.pais@oracle.com>