irqchip/irq-brcmstb-l2: Replace brcmstb_l2_mask_and_ack() by generic function

Replace brcmstb_l2_mask_and_ack() by the generic
irq_gc_mask_disable_and_ack_set().

brcmstb_l2_mask_and_ack() was added in commit 49aa6ef0
("irqchip/brcmstb-l2: Remove some processing from the handler") in
September 2017 with a comment saying it was actually generic and someone
should add it to the generic code.

commit 20608924 ("genirq: generic chip: Add
irq_gc_mask_disable_and_ack_set()") did that a few weeks later, however no
one went back and took the brcmstb variant out.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/all/20241224001727.149337-1-linux@treblig.org