clk: meson: use CONFIG_ARCH_MESON to enter meson clk directory

Use CONFIG_ARCH_MESON to let make enter the meson clock directory.
As part of a rework, CONFIG_COMMON_CLK_AMLOGIC is about to be removed.

Acked-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lkml.kernel.org/r/20190201125841.26785-3-jbrunet@baylibre.com