clk: nomadik: Remove clk.h and clkdev.h includes

Clock provider drivers generally shouldn't include clk.h because
it's the consumer API. Remove the include here because this is a
provider driver. This driver also includes clkdev.h even though
it isn't used, so drop it too and add slab.h to make sure
everything still compiles.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>