Now that we can use clk_hw pointers we don't need to have two
duplicate arrays holding the same mapping of clk index to clk_hw
pointer. Implement a custom clk_hw provider function to map the
OF specifier to the clk_hw instance for it.

Cc: Alex Elder <elder@linaro.org>
Signed-off-by: Stephen Boyd <stephen.boyd@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>