UBUNTU: SAUCE: arm64: cpu_errata: Add capability to advertise Cortex-A73 erratum...

UBUNTU: SAUCE: arm64: cpu_errata: Add capability to advertise Cortex-A73 erratum 858921

BugLink: https://bugs.launchpad.net/bugs/1675509
In order to work around Cortex-A73 erratum 858921 in a subsequent
patch, add the required capability that advertise the erratum.

As the configuration option it depends on is not present yet,
this has no immediate effect.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
(cherry picked from commit b0f0a6a803aada6268a546c3faf1987e36cbb3ca
 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>