clk: sunxi: Include clk.h and remove unused clkdev.h includes

This clock provider uses the consumer API, so include clk.h
explicitly. Also remove clkdev.h in files that aren't using it
and include slab.h when clkdev.h was being used to implicitly
include it.

Cc: Chen-Yu Tsai <wens@csie.org>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>