clk: ux500: Register slimbus clock lookups for u8500

At the same time the prcc bit for the kclk is corrected to
bit 8 instead of 3.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>