arm64: dts: stratix10: add the sysmgr-syscon property from the gmac's

The gmac ethernet driver uses the "altr,sysmgr-syscon" property to
configure phy settings for the gmac controller.

Add the "altr,sysmgr-syscon" property to all gmac nodes.

This patch fixes:

[    0.917530] socfpga-dwmac ff800000.ethernet: No sysmgr-syscon node found
[    0.924209] socfpga-dwmac ff800000.ethernet: Unable to parse OF data

Cc: stable@vger.kernel.org
Reported-by: Ley Foon Tan <ley.foon.tan@intel.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>

arch/arm64/boot/dts/altera/socfpga_stratix10.dtsi

@@ -162,6 +162,7 @@ gmac0: ethernet@ff800000 {
 			rx-fifo-depth = <16384>;
 			snps,multicast-filter-bins = <256>;
 			iommus = <&smmu 1>;
+			altr,sysmgr-syscon = <&sysmgr 0x44 0>;
 			status = "disabled";
 		};
 
@@ -179,6 +180,7 @@ gmac1: ethernet@ff802000 {
 			rx-fifo-depth = <16384>;
 			snps,multicast-filter-bins = <256>;
 			iommus = <&smmu 2>;
+			altr,sysmgr-syscon = <&sysmgr 0x48 0>;
 			status = "disabled";
 		};
 
@@ -196,6 +198,7 @@ gmac2: ethernet@ff804000 {
 			rx-fifo-depth = <16384>;
 			snps,multicast-filter-bins = <256>;
 			iommus = <&smmu 3>;
+			altr,sysmgr-syscon = <&sysmgr 0x4c 0>;
 			status = "disabled";
 		};