rockchip: rk356x: Enable poweroff command

With PMIC_RK8XX, SYSRESET and CMD_POWEROFF options enabled it is
possible to power down a board using the poweroff command and turn the
board back on using a power button.

Enable the poweroff command on RK356x boards that have a button wired
to PMIC pwron.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/configs/rock-3a-rk3568_defconfig b/configs/rock-3a-rk3568_defconfig
index 2c8af24..28d157d 100644
--- a/configs/rock-3a-rk3568_defconfig
+++ b/configs/rock-3a-rk3568_defconfig
@@ -49,6 +49,7 @@
 CONFIG_CMD_I2C=y
 CONFIG_CMD_MMC=y
 CONFIG_CMD_PCI=y
+CONFIG_CMD_POWEROFF=y
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_PMIC=y