irqchip/irq-bcm7120-l2: Set IRQ_LEVEL for level triggered interrupts

When support for the interrupt controller was added with a5042de2,
we forgot to update the flags to be set to contain IRQ_LEVEL. While the
flow handler is correct, the output from /proc/interrupts does not show
such interrupts as being level triggered when they are, correct that.

Fixes: a5042de2

 ("irqchip: bcm7120-l2: Add Broadcom BCM7120-style Level 2 interrupt controller")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20221216230934.2478345-3-f.fainelli@gmail.com