arm: meson: explicitly select clk drivers

The AmLogic clock controller code is used by both arm and arm64
architectures. Explicitly select the core code for all Meson (32-bit
arm) builds, and also select the Meson8b driver when that machine is
built.

Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>