arm64: dts: exynos: gs101: remove syscon compatible from pmu node

Since commit ba5095e ("mfd: syscon: Allow syscon nodes without a
"syscon" compatible") it is possible to register a regmap without the
syscon compatible in the node.

As mentioned in that commit, it's not correct to claim we are compatible
with syscon, as a MMIO regmap created by syscon won't work. Removing the
syscon compatible means syscon driver won't ever create a mmio regmap.

Note this isn't usually an issue today as exynos-pmu runs at an early
initcall so the custom regmap will have been registered first. However
changes proposed in [1] will bring -EPROBE_DEFER support to syscon allowing
this mechanism to be more robust, especially in highly modularized systems.

Technically this is a ABI break but no other platforms are
affected. Additionally (with the benefit of hindsight) a MMIO syscon has
never worked for PMU register writes, thus the ABI break is justified.

Link: https://lore.kernel.org/lkml/aQdHmrchkmOr34r3@stanley.mountain/ [1]
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Link: https://patch.msgid.link/20251114-remove-pmu-syscon-compat-v2-2-9496e8c496c7@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

Author: petegriffin

arch/arm64/boot/dts/exynos/google/gs101.dtsi

@@ -1714,7 +1714,7 @@
 		};
 
 		pmu_system_controller: system-controller@17460000 {
-			compatible = "google,gs101-pmu", "syscon";
+			compatible = "google,gs101-pmu";
 			reg = <0x17460000 0x10000>;
 			google,pmu-intr-gen-syscon = <&pmu_intr_gen>;