clk: socfpga: agilex: add clock driver for the Agilex platform

For the most part the Agilex clock structure is very similar to
Stratix10, so we re-use most of the Stratix10 clock driver.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Link: https://lkml.kernel.org/r/20200512181647.5071-5-dinguyen@kernel.org
Signed-off-by: Stephen Boyd <sboyd@kernel.org>