clk: oxnas: Refactor to make use of devm_clk_hw_register()

Make usage of static tables identified by the OF match table to
feed devm_clk_hw_register() and use of_clk_add_hw_provider().

This structure is cleaner and simplifies adding new SoC support while
having common probe and gate ops code.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20161005150752.22618-5-narmstrong@baylibre.com