MIPS: lantiq: implement support for clkdev api

MIPS: lantiq: implement support for clkdev api

This patch unifies all clock generation and gating code into one file.
All drivers will now be able to request their clocks via their device.
This patch also adds support for the clockout feature, which allows
clock generation on external pins.

Support for COMMON_CLK will be provided in the next series.

Signed-off-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3804/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>