ARM: meson: Add SMP bringup code for Meson8 and Meson8b

This adds the necessary SMP-operations and startup code to use the
additional cores on the Amlogic Meson8/Meson8m2 (both are using the same
sequence) and Meson8b (using a slightly difference sequence) SoCs.

Signed-off-by: Carlo Caione <carlo@endlessm.com>
[add Meson8/Meson8m2 support and allow taking CPU cores offline as well]
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

Signed-off-by: Kevin Hilman <khilman@baylibre.com>