clk: sunxi: Move header out of arch directory

The CCU header is only used by the DM drivers, not any platform code.
Its current location adds an artificial dependency on CONFIG_ARM and
ARCH_SUNXI, which will be problematic when adding the CCU driver for
a RISC-V sunxi platform.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>