mfd: rk8xx: Add support for RK806 power off

Use DEV_OFF bit to power off the RK806 PMIC, when system-power-controller
is used in DTS.

Signed-off-by: Ondrej Jirman <[e-mail]>
Reviewed-by: Sebastian Reichel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/mfd/rk8xx-core.c

···
 		reg = RK805_DEV_CTRL_REG;
 		bit = DEV_OFF;
 		break;
+	case RK806_ID:
+		reg = RK806_SYS_CFG3;
+		bit = DEV_OFF;
+		break;
 	case RK808_ID:
 		reg = RK808_DEVCTRL_REG,
 		bit = DEV_OFF_RST;