clocksource/drivers: Add Realtek system timer driver

clocksource/drivers: Add Realtek system timer driver

Add a system timer driver for Realtek SoCs.

This driver registers the 1 MHz global hardware counter on Realtek
platforms as a clock event device. Since this hardware counter starts
counting automatically after SoC power-on, no clock initialization is
required. Because the counter does not stop or get affected by CPU power
down, and it supports oneshot mode, it is typically used as a tick
broadcast timer.

Signed-off-by: Hao-Wen Ting <haowen.ting@realtek.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://patch.msgid.link/20251126060110.198330-3-haowen.ting@realtek.com