MIPS: Lantiq: Add missing clk_enable and clk_disable functions.

Signed-of-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/2465/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>