Some EXTI interrupts can be routed to a parent controller able to
wakeup the SoC from suspend.

Add the optional property 'wakeup-parent' to EXTI binding to
specify the wakeup capable interrupt controller.

While there, remove the obsoleted handling of child nodes for
multiple interrupt parent controller.

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Change-Id: I8628a57dbc3dc939ba8a6fd52ab090a47c08cac1
Reviewed-on: https://gerrit.st.com/c/mpu/oe/optee/optee_os/+/297943
Tested-by: Gatien CHEVALLIER <gatien.chevallier@st.com>
Reviewed-by: Gatien CHEVALLIER <gatien.chevallier@st.com>
Domain-Review: Gatien CHEVALLIER <gatien.chevallier@st.com>