clk: ux500: Copy u8500_clk_init() ready for DT enablement

Here we're using the old clock initialisation function as a template.
It's necessary to remove all of the clk_register_clkdev() calls as
they don't make sense when booting with Device Tree.

Cc: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>