dt-bindings: documentation: add clock bindings information for eASIC N5X

Document the Agilex clock bindings, and add the clock header file. The
clock header is an enumeration of all the different clocks on the eASIC
N5X platform.

Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>
Link: https://lore.kernel.org/r/20210212143059.478554-1-dinguyen@kernel.org


Signed-off-by: Stephen Boyd <sboyd@kernel.org>