clk: meson: Add G12A AO Clock + Reset Controller

Add the Amlogic G12A AO Clock and Reset controller driver handling
generation of Always-On clocks :
- AO Clocks and Reset for Always-On modules
- 32K Generation for USB and CEC
- SAR ADC controller clock

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lkml.kernel.org/r/20190212162859.20743-3-narmstrong@baylibre.com