irqchip: ls-extirq: add IRQCHIP_SKIP_SET_WAKE to the irqchip flags

commit 94f57e72bd6aeb8c21dfb4d20fec520d2d81f95f from
https://source.codeaurora.org/external/imx/linux-imx



The ls-extirq driver doesn't implement the irq_set_wake()
callback, while being wake-up capable. This results in
ugly behaviours across suspend/resume cycles.

Advertise this by adding IRQCHIP_SKIP_SET_WAKE to
the irqchip flags

Signed-off-by: Biwen Li <biwen.li@nxp.com>