boards/shields: x_nucleo_iks01a3: No irq-gpio on stm32mp157c_dk2

On stm32mp157c_dk2, the pin mapped on arduino connector pin A3
could not be used as GPIO.
As a consequence, pin "irq-gpio" from x_nucleo_iks01a3 shield
should not be used.

Use board overlay to remove it from shield definition.

Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>