clocksource/drivers: Add a goldfish-timer clocksource

Add a clocksource based on the goldfish-rtc device.

Move the timer register definition to <clocksource/timer-goldfish.h>

This kernel implementation is based on the QEMU upstream implementation:

https://git.qemu.org/?p=qemu.git;a=blob_plain;f=hw/rtc/goldfish_rtc.c

goldfish-timer is a high-precision signed 64-bit nanosecond timer.
It is part of the 'goldfish' virtual hardware platform used to run
some emulated Android systems under QEMU.
This timer only supports oneshot event.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Acked-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20220406201523.243733-4-laurent@vivier.eu
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>