MIPS: Loongson1B: Add a clockevent/clocksource using PWM Timer

This patch add a clockevent/clocksource using PWM Timer for Loongson1B,
which is based on earlier work by Tang, Haifeng.

Signed-off-by: Kelvin Cheung <keguang.zhang@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/8025/


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