ARM: ux500: Call appropriate clock initialisation based on DT or !DT booting

The ux500 platform will soon be converted to Device Tree only. When that
happens the old clock initialisation will be ripped out. In the meantime
however, we have to make a decision and call the appropriate
initialisation code manually.

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