Chromebooks will shutdown after an 8-sec press of the power button.

For x86 devices, this is done by stretching the power button pulse in common/power_button_x86.c and then letting the chipset see a 4-sec press for the last 4 sec of the press.

For ARM devices, this is done entirely in the power/*.c code.

It is useful to disable the long-press shutdown in some circumstances, such as firmware updates to sub-components such as PD power controllers and trackpad which should not be interrupted.

We could add a new flag to EC_CMD_CONFIG_POWER_BUTTON to do this.

(We've run into this issue a few times, so maybe it's worth preparing for the next time...)