As written in the datasheet the PCA955 can only handle low level irq and
not edge irq.

Without this fix the interrupt is not usable for pca955: the gpio-pca953x
driver already set the irq type as low level which is incompatible with
edge type, then the kernel prevents using the interrupt:

"irq: type mismatch, failed to map hwirq-18 for
/soc/internal-regs/gpio@18100!"

Fixes: 928413bd ("ARM: mvebu: Add Armada 388 General Purpose
Development Board support")
Cc: stable@vger.kernel.org
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>