powerpc/powernv: Query firmware for count cache flush settings

powerpc/powernv: Query firmware for count cache flush settings

Look for fw-features properties to determine the appropriate settings
for the count cache flush, and then call the generic powerpc code to
set it up based on the security feature flags.

BugLink: https://bugs.launchpad.net/bugs/1822870
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from commit 99d54754d3d5f896a8f616b0b6520662bc99d66b)
Signed-off-by: Manoj Iyer <manoj.iyer@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>