clk: meson-axg: Add AO Clock and Reset controller driver

Adds a Clock and Reset controller driver for the Always-On part
of the Amlogic Meson-AXG SoC.

Signed-off-by: Qiufang Dai <qiufang.dai@amlogic.com>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>