arm64: amlogic: select gxbb clk driver

The AmLogic clock controller code is used by both arm and arm64
architectures. Explicitly select the core code for all Meson (arm64)
builds, and also select the GXBB driver, since that's the way arm64 does
things.

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