clocksource/drivers/loongson1: Move PWM timer to clocksource framework

This patch moves most part of arch/mips/loongson32/common/time.c
into drivers/clocksource.

Adapt the driver to clocksource framework with devicetree support
and updates Kconfig/Makefile options.

Signed-off-by: Keguang Zhang <keguang.zhang@gmail.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230512103724.587760-4-keguang.zhang@gmail.com