irqchip/mtk-sysirq: Skip setting irq-wake

mtk-sysirq doesn't require specific logic to work with wakeup IRQs. To
allow registered IRQs to be used as a wakeup-source, add the flag
IRQCHIP_SKIP_SET_WAKE.

Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210707062004.782787-1-msp@baylibre.com