clk: meson: g12a: add peripheral clock controller

Add the peripheral clock controller found in the g12a SoC family

Signed-off-by: Jian Hu <jian.hu@amlogic.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lkml.kernel.org/r/20190201145345.6795-4-jbrunet@baylibre.com