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

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

Since commit ba5095ebbc7a ("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/
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>