sandbox: enable poweroff command

The command to shut down a device is 'poweroff'. It is a deficit of the
sandbox that it does not support resetting yet but shuts down upong seeing
the 'reset' command.

Once the sandbox properly supports reset we need the 'poweroff' command to
leave the sandbox.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/Kconfig b/arch/Kconfig
index 3b9fcce..18de8d8 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -92,6 +92,7 @@
 	bool "Sandbox"
 	select BOARD_LATE_INIT
 	select BZIP2
+	select CMD_POWEROFF
 	select DM
 	select DM_GPIO
 	select DM_I2C
@@ -107,7 +108,7 @@
 	select PCI_ENDPOINT
 	select SPI
 	select SUPPORT_OF_CONTROL
-	select SYSRESET_CMD_POWEROFF if CMD_POWEROFF
+	select SYSRESET_CMD_POWEROFF
 	imply BITREVERSE
 	select BLOBLIST
 	imply CMD_DM