powerpc/powernv: Tell OPAL about our MMU mode on POWER9

powerpc/powernv: Tell OPAL about our MMU mode on POWER9

BugLink: http://bugs.launchpad.net/bugs/1702159
That will allow OPAL to configure the CPU in an optimal way.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from 1c0eaf0f56d6128af7f0f252855173fcee85d202)
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>