ARM: dts: stm32: Fix STMPE1600 binding on stm32429i-eval board

To declare gpio interrupt line for STMPE1600, 2 possibilities are offered:
-use gpio binding (and then the gpiolib interface inside driver)
-use interrupt binding as each gpio-controller are also interrupt controller
 on stm32f429.

In STMPE 1600 node both (gpio and interrupt) bindings are defined.
This patch fixes this issue and use only interrupt binding.

Fixes: c04b2e72 ("ARM: dts: stm32: Enable STMPE1600 gpio expander of STM32F429-EVAL board")
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>