arm: meson: select the clock controller for Meson8

Select COMMON_CLK_MESON8B also for MACH_MESON8 since the Meson8b clock
controller driver can also be used on Meson8 SoCs now that we have a
separate compatible for it.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Acked-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>