UBUNTU: SAUCE: arm64: arch_timer: Workaround for Cortex-A73 erratum 858921

UBUNTU: SAUCE: arm64: arch_timer: Workaround for Cortex-A73 erratum 858921

BugLink: https://bugs.launchpad.net/bugs/1675509
Cortex-A73 (all versions) counter read can return a wrong value
when the counter crosses a 32bit boundary.

The workaround involves performing the read twice, and to return
one or the other depending on whether a transition has taken place.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
(cherry picked from commit 7b1f8a2afb42458f5878060aec51ad9c28cbf653
 in the timers/errata-rework branch of
 git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git)
Signed-off-by: dann frazier <dann.frazier@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>