arm64: zynqmp: Describe 25MHz fixed clock for PL GEMs

Describe 25Mhz fixed oscilator which is providing clock for PL based
ethernet IPs. Physicially it is one chip but it is described as 2 fixed
clock to be aligned with other SOM versions which were using integrated
clock generators where clocks could be adjusted via i2c (si5332 chips).

Link: https://lore.kernel.org/r/c430aeacaa76d9f61ed3f874f721a33049f45eb9.1706514396.git.michal.simek@amd.com
Signed-off-by: Michal Simek <michal.simek@amd.com>
State: pending

arch/arm64/boot/dts/xilinx/zynqmp-sck-kd-g-revA.dtso

@@ -32,6 +32,18 @@
 		#clock-cells = <0>;
 		clock-frequency = <26000000>;
 	};
+
+	clk_25_0: clock4 { /* u92/u91 - GEM2 */
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <25000000>;
+	};
+
+	clk_25_1: clock5 { /* u92/u91 - GEM3 */
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <25000000>;
+	};
 };
 
 &can0 {