clk: meson: only build selected platforms

Break the AmLogic clock code up so that only the necessary parts are
compiled and linked. The core code is selected by both arm and arm64
builds with COMMON_CLK_AMLOGIC. The individual drivers have their own
config options as well.

Tested-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>