ARM: dts: rockchip: add RK3288 suspend support

add pmu sram node for suspend, add global_pwroff pinctrl.
The pmu sram is used to store the resume code.
global_pwroff is held low level at work, it would be pull to high
when entering suspend. reference this in the board DTS file since
some boards need it.
Signed-off-by: Tony Xie <xxx@rock-chips.com>
Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Tested-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm/boot/dts/rk3288.dtsi

@@ -506,6 +506,11 @@ smp-sram@0 {
 		};
 	};
 
+	sram@ff720000 {
+		compatible = "rockchip,rk3288-pmu-sram", "mmio-sram";
+		reg = <0xff720000 0x1000>;
+	};
+
 	pmu: power-management@ff730000 {
 		compatible = "rockchip,rk3288-pmu", "syscon";
 		reg = <0xff730000 0x100>;
@@ -729,6 +734,24 @@ pcfg_pull_none: pcfg-pull-none {
 			bias-disable;
 		};
 
+		sleep {
+			global_pwroff: global-pwroff {
+				rockchip,pins = <0 0 RK_FUNC_1 &pcfg_pull_none>;
+			};
+
+			ddrio_pwroff: ddrio-pwroff {
+				rockchip,pins = <0 1 RK_FUNC_1 &pcfg_pull_none>;
+			};
+
+			ddr0_retention: ddr0-retention {
+				rockchip,pins = <0 2 RK_FUNC_1 &pcfg_pull_up>;
+			};
+
+			ddr1_retention: ddr1-retention {
+				rockchip,pins = <0 3 RK_FUNC_1 &pcfg_pull_up>;
+			};
+		};
+
 		i2c0 {
 			i2c0_xfer: i2c0-xfer {
 				rockchip,pins = <0 15 RK_FUNC_1 &pcfg_pull_none>,