arm64: zynqmp: Fix GIC compatible property

dtbs_check is showing warning around GIC compatible property as
interrupt-controller@f9010000: compatible: ['arm,gic-400', 'arm,cortex-a15-gic']
is not valid under any of the given schemas

Similar change has been done also by commit 5400cdc1
("ARM: dts: sunxi: Fix GIC compatible")
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/a50412fbb520954e4602f274f19a7ffbd1154ead.1582621224.git.michal.simek@xilinx.com

arch/arm64/boot/dts/xilinx/zynqmp.dtsi

@@ -189,7 +189,7 @@ amba_apu: amba-apu@0 {
 		ranges = <0 0 0 0 0xffffffff>;
 
 		gic: interrupt-controller@f9010000 {
-			compatible = "arm,gic-400", "arm,cortex-a15-gic";
+			compatible = "arm,gic-400";
 			#interrupt-cells = <3>;
 			reg = <0x0 0xf9010000 0x10000>,
 			      <0x0 0xf9020000 0x20000>,