clk: fixed-factor: Add hw based registration APIs

clk: fixed-factor: Add hw based registration APIs

Add registration APIs in the clk fixed-factor code to return
struct clk_hw pointers instead of struct clk pointers. This way
we hide the struct clk pointer from providers unless they need to
use consumer facing APIs.

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