arm64: dts: juno: add dedicated FPGA syscon compatible

Each syscon node must come with a dedicated/specific compatible, which
is also reported by dtbs_check:

  juno.dtb: apbregs@10000: compatible: ['syscon', 'simple-mfd'] is too short
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240518203903.119608-2-krzysztof.kozlowski@linaro.orgSigned-off-by: Sudeep Holla <sudeep.holla@arm.com>

arch/arm64/boot/dts/arm/juno-motherboard.dtsi

@@ -158,7 +158,8 @@ v2m_sysctl: sysctl@20000 {
 				};
 
 				apbregs@10000 {
-					compatible = "syscon", "simple-mfd";
+					compatible = "arm,juno-fpga-apb-regs",
+						     "syscon", "simple-mfd";
 					reg = <0x010000 0x1000>;
 					ranges = <0x0 0x10000 0x1000>;
 					#address-cells = <1>;