clk: meson: Add support for Meson clock controller

This patchset adds the infrastructure for registering and managing the
core clocks found on Amlogic MesonX SoCs. In particular:

- PLLs
- CPU clock
- Fixed rate clocks, fixed factor clocks, ...

Signed-off-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>