configs: stm32mp1: Enable BUTTON_GPIO flag for stm32mp13_defconfig

Enable BUTTON_GPIO flag for STM32MP15.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@gmail.com>
1 file changed