clk: meson: meson8b: register the built-in reset controller

The clock controller also includes some reset lines. This patch
implements a reset controller to assert and de-assert these resets.
The reset controller itself is registered early (through
CLK_OF_DECLARE_DRIVER) because it is needed very early in the boot
process (to start the secondary CPU cores).

According to the public S805 datasheet there are two more reset bits
in the HHI_SYS_CPU_CLK_CNTL0 register, which are not implemented by
this patch (as these seem to be unused in Amlogic's vendor Linux kernel
sources and their u-boot tree):
- bit 15: GEN_DIV_SOFT_RESET
- bit 14: SOFT_RESET

All information was taken from the public S805 Datasheet and Amlogic's
vendor GPL kernel sources. This patch is based on an earlier version
submitted by Carlo Caione.

Suggested-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>