arm64: dts: imx8mp: Add SNVS LPGPR

Add SNVS LPGPR bindings to MX8M Plus, the LPGPR is used to store
e.g. boot counter.
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Fabio Estevam <festevam@denx.de>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mp.dtsi

@@ -470,6 +470,11 @@ snvs_pwrkey: snvs-powerkey {
 					wakeup-source;
 					status = "disabled";
 				};
+
+				snvs_lpgpr: snvs-lpgpr {
+					compatible = "fsl,imx8mp-snvs-lpgpr",
+						     "fsl,imx7d-snvs-lpgpr";
+				};
 			};
 
 			clk: clock-controller@30380000 {