clk: meson: clean-up meson clock configuration

Clean the dependencies in meson clock Kconfig.
CLK_AMLOGIC should actually select CLK_REGMAP_MESON which it uses. Also,
each platform should select CLK_AMLOGIC, so everything is properly turned
on when the platform Kconfig enable each configuration flag

Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>