clk: axm5516: Migrate to clk_hw based OF and registration APIs

Now that we have clk_hw based provider APIs to register clks, we
can get rid of struct clk pointers while registering clks in
these drivers, allowing us to move closer to a clear split of
consumer and provider clk APIs. Make thing simple by using the
existing clk_hw array and implementing a custom DT clk provider
get function to map the clk spec id to a clk_hw pointer.

Cc: Anders Berg <anders.berg@lsi.com>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>