irqchip/gic-v3: Use readl_relaxed_poll_timeout_atomic()

Replace the open coded register polling loop with
readl_relaxed_poll_timeout_atomic() which provides the same functionality.

Signed-off-by: Dawei Li <dawei.li@shingroup.cn>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240122085716.2999875-2-dawei.li@shingroup.cn