At the moment there is no software configuration that can enable generation of WDT_RESET_OUT signal.
But the register PMC_IMPL_RST_REQ_CONFIG_0(0xc360114) can be written from BPMP.
Set the value using command
echo “mw 0xc360114 1” > /sys/kernel/debug/bpmp/debug/cons
Pinmux should be updated to configure WDT_RESET_OUT pin (SOC_GPIO23) as WDT_RESET_OUTA
WDT reset after this will pull the WDT_RESET_OUT signal low. But the system will reboot only when SYS_RESET_N is toggled.
So the external MCU will have to capture WDT_RESET_OUT signal going low and then drive SYS_RESET_N to reboot the system.