apps/system/poweroff: add a dependancy with BOARDCTL_POWEROFF
Poweroff application can be enabled when board supports poweroff functionality.
This commit fixs below:
/os/../build/output/libraries/libapps.a(poweroff.o): In function `poweroff_main':
/apps/system/poweroff/poweroff.c:68: undefined reference to `board_power_off'
config SYSTEM_POWEROFF
bool "Power-Off command"
default n
+ depends on BOARDCTL_POWEROFF
---help---
Enable support for the TASH poweroff command. NOTE: This option
provides the TASH power-off command only. It requires board-specific
